diff --git a/gcloud/_helpers.py b/gcloud/_helpers.py
index 7e0644ef7cb7..664c867b1c61 100644
--- a/gcloud/_helpers.py
+++ b/gcloud/_helpers.py
@@ -16,6 +16,7 @@
 This module is not part of the public API surface of `gcloud`.
 """
 
+import calendar
 import datetime
 import os
 import socket
@@ -36,6 +37,7 @@ class Local(object):
 from gcloud.environment_vars import PROJECT
 
 
+_NOW = datetime.datetime.utcnow  # To be replaced by tests.
 _RFC3339_MICROS = '%Y-%m-%dT%H:%M:%S.%fZ'
 
 
@@ -207,7 +209,65 @@ def _determine_default_project(project=None):
     return project
 
 
+def _millis(when):
+    """Convert a zone-aware datetime to integer milliseconds.
+
+    :type when: :class:`datetime.datetime`
+    :param when: the datetime to convert
+
+    :rtype: integer
+    :returns: milliseconds since epoch for ``when``
+    """
+    micros = _microseconds_from_datetime(when)
+    return micros // 1000
+
+
+def _datetime_from_microseconds(value):
+    """Convert timestamp to datetime, assuming UTC.
+
+    :type value: float
+    :param value: The timestamp to convert
+
+    :rtype: :class:`datetime.datetime`
+    :returns: The datetime object created from the value.
+    """
+    return _EPOCH + datetime.timedelta(microseconds=value)
+
+
+def _microseconds_from_datetime(value):
+    """Convert non-none datetime to microseconds.
+
+    :type value: :class:`datetime.datetime`
+    :param value: The timestamp to convert.
+
+    :rtype: integer
+    :returns: The timestamp, in microseconds.
+    """
+    if not value.tzinfo:
+        value = value.replace(tzinfo=UTC)
+    # Regardless of what timezone is on the value, convert it to UTC.
+    value = value.astimezone(UTC)
+    # Convert the datetime to a microsecond timestamp.
+    return int(calendar.timegm(value.timetuple()) * 1e6) + value.microsecond
+
+
+def _millis_from_datetime(value):
+    """Convert non-none datetime to timestamp, assuming UTC.
+
+    :type value: :class:`datetime.datetime`, or None
+    :param value: the timestamp
+
+    :rtype: integer, or ``NoneType``
+    :returns: the timestamp, in milliseconds, or None
+    """
+    if value is not None:
+        return _millis(value)
+
+
 try:
     from pytz import UTC  # pylint: disable=unused-import
 except ImportError:
     UTC = _UTC()  # Singleton instance to be used throughout.
+
+# Need to define _EPOCH at the end of module since it relies on UTC.
+_EPOCH = datetime.datetime.utcfromtimestamp(0).replace(tzinfo=UTC)
diff --git a/gcloud/bigquery/_helpers.py b/gcloud/bigquery/_helpers.py
deleted file mode 100644
index df6215721c7d..000000000000
--- a/gcloud/bigquery/_helpers.py
+++ /dev/null
@@ -1,79 +0,0 @@
-# Copyright 2015 Google Inc. All rights reserved.
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#     http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-
-"""BigQuery utility functions."""
-
-
-import datetime
-import sys
-
-from gcloud._helpers import UTC
-
-
-_EPOCH = datetime.datetime.utcfromtimestamp(0).replace(tzinfo=UTC)
-
-
-def _millis(when):
-    """Convert a zone-aware datetime to integer milliseconds.
-
-    :type when: ``datetime.datetime``
-    :param when: the datetime to convert
-
-    :rtype: integer
-    :returns: milliseconds since epoch for ``when``
-    """
-    return int(_total_seconds(when - _EPOCH) * 1000)
-
-
-def _datetime_from_prop(value):
-    """Convert non-none timestamp to datetime, assuming UTC.
-
-    :rtype: ``datetime.datetime``, or ``NoneType``
-    """
-    if value is not None:
-        # back-end returns timestamps as milliseconds since the epoch
-        seconds = int(value / 1000.0)
-        microseconds = 1000.0 * (value - 1000 * seconds)
-        return (
-            _EPOCH +
-            datetime.timedelta(seconds=seconds, microseconds=microseconds)
-        )
-
-
-def _prop_from_datetime(value):
-    """Convert non-none datetime to timestamp, assuming UTC.
-
-    :type value: ``datetime.datetime``, or None
-    :param value: the timestamp
-
-    :rtype: integer, or ``NoneType``
-    :returns: the timestamp, in milliseconds, or None
-    """
-    if value is not None:
-        if value.tzinfo is None:
-            # Assume UTC
-            value = value.replace(tzinfo=UTC)
-        # back-end wants timestamps as milliseconds since the epoch
-        return _millis(value)
-
-
-if sys.version_info[:2] < (2, 7):
-    def _total_seconds(offset):  # pragma: NO COVER
-        """Backport of timedelta.total_seconds() from python 2.7+."""
-        seconds = offset.days * 24 * 60 * 60 + offset.seconds
-        microseconds = seconds * 10**6 + offset.microseconds
-        return microseconds / (10**6 * 1.0)
-else:
-    def _total_seconds(offset):
-        return offset.total_seconds()
diff --git a/gcloud/bigquery/dataset.py b/gcloud/bigquery/dataset.py
index 47d799e33186..82d60c6dfec2 100644
--- a/gcloud/bigquery/dataset.py
+++ b/gcloud/bigquery/dataset.py
@@ -15,8 +15,8 @@
 """Define API Datasets."""
 import six
 
+from gcloud._helpers import _datetime_from_microseconds
 from gcloud.exceptions import NotFound
-from gcloud.bigquery._helpers import _datetime_from_prop
 from gcloud.bigquery.table import Table
 
 
@@ -114,7 +114,10 @@ def created(self):
         :rtype: ``datetime.datetime``, or ``NoneType``
         :returns: the creation time (None until set from the server).
         """
-        return _datetime_from_prop(self._properties.get('creationTime'))
+        creation_time = self._properties.get('creationTime')
+        if creation_time is not None:
+            # creation_time will be in milliseconds.
+            return _datetime_from_microseconds(1000.0 * creation_time)
 
     @property
     def dataset_id(self):
@@ -141,7 +144,10 @@ def modified(self):
         :rtype: ``datetime.datetime``, or ``NoneType``
         :returns: the modification time (None until set from the server).
         """
-        return _datetime_from_prop(self._properties.get('lastModifiedTime'))
+        modified_time = self._properties.get('lastModifiedTime')
+        if modified_time is not None:
+            # modified_time will be in milliseconds.
+            return _datetime_from_microseconds(1000.0 * modified_time)
 
     @property
     def self_link(self):
diff --git a/gcloud/bigquery/table.py b/gcloud/bigquery/table.py
index ee2d40cb8a2a..6f1c09c2ad99 100644
--- a/gcloud/bigquery/table.py
+++ b/gcloud/bigquery/table.py
@@ -18,9 +18,9 @@
 
 import six
 
+from gcloud._helpers import _datetime_from_microseconds
+from gcloud._helpers import _millis_from_datetime
 from gcloud.exceptions import NotFound
-from gcloud.bigquery._helpers import _datetime_from_prop
-from gcloud.bigquery._helpers import _prop_from_datetime
 
 
 _MARKER = object()
@@ -116,7 +116,10 @@ def created(self):
         :rtype: ``datetime.datetime``, or ``NoneType``
         :returns: the creation time (None until set from the server).
         """
-        return _datetime_from_prop(self._properties.get('creationTime'))
+        creation_time = self._properties.get('creationTime')
+        if creation_time is not None:
+            # creation_time will be in milliseconds.
+            return _datetime_from_microseconds(1000.0 * creation_time)
 
     @property
     def etag(self):
@@ -134,7 +137,10 @@ def modified(self):
         :rtype: ``datetime.datetime``, or ``NoneType``
         :returns: the modification time (None until set from the server).
         """
-        return _datetime_from_prop(self._properties.get('lastModifiedTime'))
+        modified_time = self._properties.get('lastModifiedTime')
+        if modified_time is not None:
+            # modified_time will be in milliseconds.
+            return _datetime_from_microseconds(1000.0 * modified_time)
 
     @property
     def num_bytes(self):
@@ -212,7 +218,10 @@ def expires(self):
         :rtype: ``datetime.datetime``, or ``NoneType``
         :returns: the expiration time, or None
         """
-        return _datetime_from_prop(self._properties.get('expirationTime'))
+        expiration_time = self._properties.get('expirationTime')
+        if expiration_time is not None:
+            # expiration_time will be in milliseconds.
+            return _datetime_from_microseconds(1000.0 * expiration_time)
 
     @expires.setter
     def expires(self, value):
@@ -223,7 +232,7 @@ def expires(self, value):
         """
         if not isinstance(value, datetime.datetime) and value is not None:
             raise ValueError("Pass a datetime, or None")
-        self._properties['expirationTime'] = _prop_from_datetime(value)
+        self._properties['expirationTime'] = _millis_from_datetime(value)
 
     @property
     def friendly_name(self):
@@ -405,7 +414,7 @@ def _build_resource(self):
             resource['description'] = self.description
 
         if self.expires is not None:
-            value = _prop_from_datetime(self.expires)
+            value = _millis_from_datetime(self.expires)
             resource['expirationTime'] = value
 
         if self.friendly_name is not None:
@@ -518,7 +527,7 @@ def patch(self,
             if (not isinstance(expires, datetime.datetime) and
                     expires is not None):
                 raise ValueError("Pass a datetime, or None")
-            partial['expirationTime'] = _prop_from_datetime(expires)
+            partial['expirationTime'] = _millis_from_datetime(expires)
 
         if description is not _MARKER:
             partial['description'] = description
@@ -678,7 +687,7 @@ def insert_data(self,
 
             for field, value in zip(self._schema, row):
                 if field.field_type == 'TIMESTAMP':
-                    value = _prop_from_datetime(value)
+                    value = _millis_from_datetime(value)
                 row_info[field.name] = value
 
             info = {'json': row_info}
@@ -727,7 +736,8 @@ def _bool_from_json(value, field):
 
 def _datetime_from_json(value, field):
     if _not_null(value, field):
-        return _datetime_from_prop(float(value))
+        # Field value will be in milliseconds.
+        return _datetime_from_microseconds(1000.0 * float(value))
 
 
 def _record_from_json(value, field):
diff --git a/gcloud/bigquery/test__helpers.py b/gcloud/bigquery/test__helpers.py
deleted file mode 100644
index ee97717ef9f6..000000000000
--- a/gcloud/bigquery/test__helpers.py
+++ /dev/null
@@ -1,103 +0,0 @@
-# Copyright 2015 Google Inc. All rights reserved.
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#     http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-
-import unittest2
-
-
-class Test__millis(unittest2.TestCase):
-
-    def _callFUT(self, value):
-        from gcloud.bigquery._helpers import _millis
-        return _millis(value)
-
-    def test_one_second_from_epoch(self):
-        import datetime
-        from gcloud._helpers import UTC
-
-        WHEN = datetime.datetime(1970, 1, 1, 0, 0, 1, tzinfo=UTC)
-        self.assertEqual(self._callFUT(WHEN), 1000)
-
-
-class Test__datetime_from_prop(unittest2.TestCase):
-
-    def _callFUT(self, value):
-        from gcloud.bigquery._helpers import _datetime_from_prop
-        return _datetime_from_prop(value)
-
-    def test_w_none(self):
-        self.assertTrue(self._callFUT(None) is None)
-
-    def test_w_millis(self):
-        import datetime
-        from gcloud._helpers import UTC
-        from gcloud.bigquery._helpers import _total_seconds
-
-        NOW = datetime.datetime(2015, 7, 29, 17, 45, 21, 123456,
-                                tzinfo=UTC)
-        EPOCH = datetime.datetime(1970, 1, 1, tzinfo=UTC)
-        MILLIS = _total_seconds(NOW - EPOCH) * 1000
-        self.assertEqual(self._callFUT(MILLIS), NOW)
-
-
-class Test__prop_from_datetime(unittest2.TestCase):
-
-    def _callFUT(self, value):
-        from gcloud.bigquery._helpers import _prop_from_datetime
-        return _prop_from_datetime(value)
-
-    def test_w_none(self):
-        self.assertTrue(self._callFUT(None) is None)
-
-    def test_w_utc_datetime(self):
-        import datetime
-        from gcloud._helpers import UTC
-        from gcloud.bigquery._helpers import _total_seconds
-
-        NOW = datetime.datetime.utcnow().replace(tzinfo=UTC)
-        EPOCH = datetime.datetime(1970, 1, 1, tzinfo=UTC)
-        MILLIS = int(_total_seconds(NOW - EPOCH) * 1000)
-        result = self._callFUT(NOW)
-        self.assertTrue(isinstance(result, int))
-        self.assertEqual(result, MILLIS)
-
-    def test_w_non_utc_datetime(self):
-        import datetime
-        from gcloud._helpers import UTC
-        from gcloud._helpers import _UTC
-        from gcloud.bigquery._helpers import _total_seconds
-
-        class CET(_UTC):
-            _tzname = 'CET'
-            _utcoffset = datetime.timedelta(hours=-1)
-
-        zone = CET()
-        NOW = datetime.datetime(2015, 7, 28, 16, 34, 47, tzinfo=zone)
-        EPOCH = datetime.datetime(1970, 1, 1, tzinfo=UTC)
-        MILLIS = int(_total_seconds(NOW - EPOCH) * 1000)
-        result = self._callFUT(NOW)
-        self.assertTrue(isinstance(result, int))
-        self.assertEqual(result, MILLIS)
-
-    def test_w_naive_datetime(self):
-        import datetime
-        from gcloud._helpers import UTC
-        from gcloud.bigquery._helpers import _total_seconds
-
-        NOW = datetime.datetime.utcnow()
-        UTC_NOW = NOW.replace(tzinfo=UTC)
-        EPOCH = datetime.datetime(1970, 1, 1, tzinfo=UTC)
-        MILLIS = int(_total_seconds(UTC_NOW - EPOCH) * 1000)
-        result = self._callFUT(NOW)
-        self.assertTrue(isinstance(result, int))
-        self.assertEqual(result, MILLIS)
diff --git a/gcloud/bigquery/test_table.py b/gcloud/bigquery/test_table.py
index 3dd5394da5cd..530f55a9ead0 100644
--- a/gcloud/bigquery/test_table.py
+++ b/gcloud/bigquery/test_table.py
@@ -240,7 +240,7 @@ def test_schema_setter(self):
     def test_props_set_by_server(self):
         import datetime
         from gcloud._helpers import UTC
-        from gcloud.bigquery._helpers import _millis
+        from gcloud._helpers import _millis
 
         CREATED = datetime.datetime(2015, 7, 29, 12, 13, 22, tzinfo=UTC)
         MODIFIED = datetime.datetime(2015, 7, 29, 14, 47, 15, tzinfo=UTC)
@@ -516,8 +516,8 @@ def test_create_w_bound_client(self):
     def test_create_w_alternate_client(self):
         import datetime
         from gcloud._helpers import UTC
+        from gcloud._helpers import _millis
         from gcloud.bigquery.table import SchemaField
-        from gcloud.bigquery._helpers import _millis
 
         PATH = 'projects/%s/datasets/%s/tables' % (self.PROJECT, self.DS_NAME)
         DESCRIPTION = 'DESCRIPTION'
@@ -716,7 +716,7 @@ def test_patch_w_bound_client(self):
     def test_patch_w_alternate_client(self):
         import datetime
         from gcloud._helpers import UTC
-        from gcloud.bigquery._helpers import _millis
+        from gcloud._helpers import _millis
         from gcloud.bigquery.table import SchemaField
 
         PATH = 'projects/%s/datasets/%s/tables/%s' % (
@@ -825,7 +825,7 @@ def test_update_w_bound_client(self):
     def test_update_w_alternate_client(self):
         import datetime
         from gcloud._helpers import UTC
-        from gcloud.bigquery._helpers import _millis
+        from gcloud._helpers import _millis
         from gcloud.bigquery.table import SchemaField
 
         PATH = 'projects/%s/datasets/%s/tables/%s' % (
@@ -914,7 +914,7 @@ def test_fetch_data_w_bound_client(self):
         import datetime
         from gcloud._helpers import UTC
         from gcloud.bigquery.table import SchemaField
-        from gcloud.bigquery._helpers import _prop_from_datetime
+        from gcloud._helpers import _millis_from_datetime
 
         PATH = 'projects/%s/datasets/%s/tables/%s/data' % (
             self.PROJECT, self.DS_NAME, self.TABLE_NAME)
@@ -932,17 +932,17 @@ def test_fetch_data_w_bound_client(self):
                 {'f': [
                     {'v': 'Phred Phlyntstone'},
                     {'v': '32'},
-                    {'v': _prop_from_datetime(WHEN)},
+                    {'v': _millis_from_datetime(WHEN)},
                 ]},
                 {'f': [
                     {'v': 'Bharney Rhubble'},
                     {'v': '33'},
-                    {'v': _prop_from_datetime(WHEN_1)},
+                    {'v': _millis_from_datetime(WHEN_1)},
                 ]},
                 {'f': [
                     {'v': 'Wylma Phlyntstone'},
                     {'v': '29'},
-                    {'v': _prop_from_datetime(WHEN_2)},
+                    {'v': _millis_from_datetime(WHEN_2)},
                 ]},
                 {'f': [
                     {'v': 'Bhettye Rhubble'},
@@ -1145,7 +1145,7 @@ def test_fetch_data_w_record_schema(self):
     def test_insert_data_w_bound_client(self):
         import datetime
         from gcloud._helpers import UTC
-        from gcloud.bigquery._helpers import _prop_from_datetime
+        from gcloud._helpers import _millis_from_datetime
         from gcloud.bigquery.table import SchemaField
 
         WHEN_TS = 1437767599.006
@@ -1171,7 +1171,7 @@ def test_insert_data_w_bound_client(self):
         def _row_data(row):
             return {'full_name': row[0],
                     'age': row[1],
-                    'joined': _prop_from_datetime(row[2])}
+                    'joined': _millis_from_datetime(row[2])}
 
         SENT = {
             'rows': [{'json': _row_data(row)} for row in ROWS],
diff --git a/gcloud/credentials.py b/gcloud/credentials.py
index 843937021eef..56eca8fc6612 100644
--- a/gcloud/credentials.py
+++ b/gcloud/credentials.py
@@ -15,7 +15,6 @@
 """A simple wrapper around the OAuth2 credentials library."""
 
 import base64
-import calendar
 import datetime
 import six
 from six.moves.urllib.parse import urlencode  # pylint: disable=F0401
@@ -40,6 +39,8 @@ class _GAECreds(object):
         """Dummy class if not in App Engine environment."""
 
 from gcloud._helpers import UTC
+from gcloud._helpers import _NOW
+from gcloud._helpers import _microseconds_from_datetime
 
 
 def get_credentials():
@@ -256,14 +257,6 @@ def _get_signed_query_params(credentials, expiration, string_to_sign):
     }
 
 
-def _utcnow():  # pragma: NO COVER testing replaces
-    """Returns current time as UTC datetime.
-
-    NOTE: on the module namespace so tests can replace it.
-    """
-    return datetime.datetime.utcnow()
-
-
 def _get_expiration_seconds(expiration):
     """Convert 'expiration' to a number of seconds in the future.
 
@@ -275,20 +268,13 @@ def _get_expiration_seconds(expiration):
     """
     # If it's a timedelta, add it to `now` in UTC.
     if isinstance(expiration, datetime.timedelta):
-        now = _utcnow().replace(tzinfo=UTC)
+        now = _NOW().replace(tzinfo=UTC)
         expiration = now + expiration
 
     # If it's a datetime, convert to a timestamp.
     if isinstance(expiration, datetime.datetime):
-        # Make sure the timezone on the value is UTC
-        # (either by converting or replacing the value).
-        if expiration.tzinfo:
-            expiration = expiration.astimezone(UTC)
-        else:
-            expiration = expiration.replace(tzinfo=UTC)
-
-        # Turn the datetime into a timestamp (seconds, not microseconds).
-        expiration = int(calendar.timegm(expiration.timetuple()))
+        micros = _microseconds_from_datetime(expiration)
+        expiration = micros // 10**6
 
     if not isinstance(expiration, six.integer_types):
         raise TypeError('Expected an integer timestamp, datetime, or '
diff --git a/gcloud/datastore/helpers.py b/gcloud/datastore/helpers.py
index ccf428c83a47..427df84e726f 100644
--- a/gcloud/datastore/helpers.py
+++ b/gcloud/datastore/helpers.py
@@ -17,13 +17,13 @@
 The non-private functions are part of the API.
 """
 
-import calendar
 import datetime
 
 from google.protobuf.internal.type_checkers import Int64ValueChecker
 import six
 
-from gcloud._helpers import UTC
+from gcloud._helpers import _datetime_from_microseconds
+from gcloud._helpers import _microseconds_from_datetime
 from gcloud.datastore import _datastore_v1_pb2 as datastore_pb
 from gcloud.datastore.entity import Entity
 from gcloud.datastore.key import Key
@@ -182,14 +182,7 @@ def _pb_attr_value(val):
 
     if isinstance(val, datetime.datetime):
         name = 'timestamp_microseconds'
-        # If the datetime is naive (no timezone), consider that it was
-        # intended to be UTC and replace the tzinfo to that effect.
-        if not val.tzinfo:
-            val = val.replace(tzinfo=UTC)
-        # Regardless of what timezone is on the value, convert it to UTC.
-        val = val.astimezone(UTC)
-        # Convert the datetime to a microsecond timestamp.
-        value = int(calendar.timegm(val.timetuple()) * 1e6) + val.microsecond
+        value = _microseconds_from_datetime(val)
     elif isinstance(val, Key):
         name, value = 'key', val.to_protobuf()
     elif isinstance(val, bool):
@@ -231,9 +224,7 @@ def _get_value_from_value_pb(value_pb):
     result = None
     if value_pb.HasField('timestamp_microseconds_value'):
         microseconds = value_pb.timestamp_microseconds_value
-        naive = (datetime.datetime.utcfromtimestamp(0) +
-                 datetime.timedelta(microseconds=microseconds))
-        result = naive.replace(tzinfo=UTC)
+        result = _datetime_from_microseconds(microseconds)
 
     elif value_pb.HasField('key_value'):
         result = key_from_protobuf(value_pb.key_value)
@@ -292,7 +283,7 @@ def _set_protobuf_value(value_pb, val):
     :type value_pb: :class:`gcloud.datastore._datastore_v1_pb2.Value`
     :param value_pb: The value protobuf to which the value is being assigned.
 
-    :type val: `datetime.datetime`, boolean, float, integer, string,
+    :type val: :class:`datetime.datetime`, boolean, float, integer, string,
                :class:`gcloud.datastore.key.Key`,
                :class:`gcloud.datastore.entity.Entity`,
     :param val: The value to be assigned.
diff --git a/gcloud/pubsub/topic.py b/gcloud/pubsub/topic.py
index 78582c5a7aea..6ac05ee243f0 100644
--- a/gcloud/pubsub/topic.py
+++ b/gcloud/pubsub/topic.py
@@ -15,15 +15,13 @@
 """Define API Topics."""
 
 import base64
-import datetime
 
+from gcloud._helpers import _NOW
 from gcloud._helpers import _RFC3339_MICROS
 from gcloud.exceptions import NotFound
 from gcloud.pubsub._helpers import topic_name_from_path
 from gcloud.pubsub.subscription import Subscription
 
-_NOW = datetime.datetime.utcnow
-
 
 class Topic(object):
     """Topics are targets to which messages can be published.
diff --git a/gcloud/test__helpers.py b/gcloud/test__helpers.py
index 72715470f6f2..e248d687220d 100644
--- a/gcloud/test__helpers.py
+++ b/gcloud/test__helpers.py
@@ -251,6 +251,106 @@ def test_prod(self):
         self.assertEqual(callers, ['prod_mock'])
 
 
+class Test__millis(unittest2.TestCase):
+
+    def _callFUT(self, value):
+        from gcloud._helpers import _millis
+        return _millis(value)
+
+    def test_one_second_from_epoch(self):
+        import datetime
+        from gcloud._helpers import UTC
+
+        WHEN = datetime.datetime(1970, 1, 1, 0, 0, 1, tzinfo=UTC)
+        self.assertEqual(self._callFUT(WHEN), 1000)
+
+
+class Test__microseconds_from_datetime(unittest2.TestCase):
+
+    def _callFUT(self, value):
+        from gcloud._helpers import _microseconds_from_datetime
+        return _microseconds_from_datetime(value)
+
+    def test_it(self):
+        import datetime
+
+        microseconds = 314159
+        timestamp = datetime.datetime(1970, 1, 1, hour=0,
+                                      minute=0, second=0,
+                                      microsecond=microseconds)
+        result = self._callFUT(timestamp)
+        self.assertEqual(result, microseconds)
+
+
+class Test__millis_from_datetime(unittest2.TestCase):
+
+    def _callFUT(self, value):
+        from gcloud._helpers import _millis_from_datetime
+        return _millis_from_datetime(value)
+
+    def test_w_none(self):
+        self.assertTrue(self._callFUT(None) is None)
+
+    def test_w_utc_datetime(self):
+        import datetime
+        from gcloud._helpers import UTC
+        from gcloud._helpers import _microseconds_from_datetime
+
+        NOW = datetime.datetime.utcnow().replace(tzinfo=UTC)
+        NOW_MICROS = _microseconds_from_datetime(NOW)
+        MILLIS = NOW_MICROS // 1000
+        result = self._callFUT(NOW)
+        self.assertTrue(isinstance(result, int))
+        self.assertEqual(result, MILLIS)
+
+    def test_w_non_utc_datetime(self):
+        import datetime
+        from gcloud._helpers import _UTC
+        from gcloud._helpers import _microseconds_from_datetime
+
+        class CET(_UTC):
+            _tzname = 'CET'
+            _utcoffset = datetime.timedelta(hours=-1)
+
+        zone = CET()
+        NOW = datetime.datetime(2015, 7, 28, 16, 34, 47, tzinfo=zone)
+        NOW_MICROS = _microseconds_from_datetime(NOW)
+        MILLIS = NOW_MICROS // 1000
+        result = self._callFUT(NOW)
+        self.assertTrue(isinstance(result, int))
+        self.assertEqual(result, MILLIS)
+
+    def test_w_naive_datetime(self):
+        import datetime
+        from gcloud._helpers import UTC
+        from gcloud._helpers import _microseconds_from_datetime
+
+        NOW = datetime.datetime.utcnow()
+        UTC_NOW = NOW.replace(tzinfo=UTC)
+        UTC_NOW_MICROS = _microseconds_from_datetime(UTC_NOW)
+        MILLIS = UTC_NOW_MICROS // 1000
+        result = self._callFUT(NOW)
+        self.assertTrue(isinstance(result, int))
+        self.assertEqual(result, MILLIS)
+
+
+class Test__datetime_from_microseconds(unittest2.TestCase):
+
+    def _callFUT(self, value):
+        from gcloud._helpers import _datetime_from_microseconds
+        return _datetime_from_microseconds(value)
+
+    def test_it(self):
+        import datetime
+        from gcloud._helpers import UTC
+        from gcloud._helpers import _microseconds_from_datetime
+
+        NOW = datetime.datetime(2015, 7, 29, 17, 45, 21, 123456,
+                                tzinfo=UTC)
+        NOW_MICROS = _microseconds_from_datetime(NOW)
+        self.assertEqual(self._callFUT(NOW_MICROS), NOW)
+
+
 class _AppIdentity(object):
 
     def __init__(self, app_id):
diff --git a/gcloud/test_credentials.py b/gcloud/test_credentials.py
index 33987f5db74c..06d4d50afb52 100644
--- a/gcloud/test_credentials.py
+++ b/gcloud/test_credentials.py
@@ -541,7 +541,7 @@ def test_w_timedelta_seconds(self):
         utc_seconds = self._utc_seconds(dummy_utcnow)
         expiration_as_delta = datetime.timedelta(seconds=10)
 
-        with _Monkey(MUT, _utcnow=lambda: dummy_utcnow):
+        with _Monkey(MUT, _NOW=lambda: dummy_utcnow):
             result = self._callFUT(expiration_as_delta)
 
         self.assertEqual(result, utc_seconds + 10)
@@ -555,7 +555,7 @@ def test_w_timedelta_days(self):
         utc_seconds = self._utc_seconds(dummy_utcnow)
         expiration_as_delta = datetime.timedelta(days=1)
 
-        with _Monkey(MUT, _utcnow=lambda: dummy_utcnow):
+        with _Monkey(MUT, _NOW=lambda: dummy_utcnow):
             result = self._callFUT(expiration_as_delta)
 
         self.assertEqual(result, utc_seconds + 86400)