diff --git a/public/main/exercise/exercise_reminder.php b/public/main/exercise/exercise_reminder.php
index 5742bb17140..a74fc58e550 100644
--- a/public/main/exercise/exercise_reminder.php
+++ b/public/main/exercise/exercise_reminder.php
@@ -50,7 +50,7 @@
 
 if ($time_control) {
     // Get time left for expiring time
-    $time_left = api_strtotime($clock_expired_time->format('Y-m-d H:i:s'), 'UTC') - time();
+    $time_left = api_strtotime($clock_expired_time, 'UTC') - time();
     $htmlHeadXtra[] = $objExercise->showTimeControlJS($time_left);
 }
 
diff --git a/public/main/exercise/exercise_submit.php b/public/main/exercise/exercise_submit.php
index adc9a917218..3ff000b0bbe 100644
--- a/public/main/exercise/exercise_submit.php
+++ b/public/main/exercise/exercise_submit.php
@@ -431,11 +431,11 @@
 
         $clock_expired_time = api_get_utc_datetime($expected_time, false, true);
         if ($debug) {
-            error_log('5.3. $expected_time '.$clock_expired_time);
+            error_log('5.3. $expected_time '.$clock_expired_time->format('Y-m-d H:i:s'));
         }
 
         //Sessions  that contain the expired time
-        $_SESSION['expired_time'][$current_expired_time_key] = $clock_expired_time;
+        $_SESSION['expired_time'][$current_expired_time_key] = $clock_expired_time->format('Y-m-d H:i:s');
         if ($debug) {
             error_log(
                 '5.4. Setting the $_SESSION[expired_time]: '.$_SESSION['expired_time'][$current_expired_time_key]
diff --git a/public/main/exercise/overview.php b/public/main/exercise/overview.php
index 764b60554c3..cbc14bc70ea 100644
--- a/public/main/exercise/overview.php
+++ b/public/main/exercise/overview.php
@@ -69,7 +69,7 @@
 $htmlHeadXtra[] = api_get_build_js('legacy_exercise.js');
 if ($time_control) {
     // Get time left for expiring time
-    $time_left = api_strtotime($clock_expired_time->format('Y-m-d H:i:s'), 'UTC') - time();
+    $time_left = api_strtotime($clock_expired_time, 'UTC') - time();
     /*$htmlHeadXtra[] = api_get_css(api_get_path(WEB_LIBRARY_PATH).'javascript/epiclock/stylesheet/jquery.epiclock.css');
     $htmlHeadXtra[] = api_get_css(api_get_path(WEB_LIBRARY_PATH).'javascript/epiclock/renderers/minute/epiclock.minute.css');
     $htmlHeadXtra[] = api_get_js('epiclock/javascript/jquery.dateformat.min.js');
@@ -145,7 +145,7 @@
 );
 
 if ($time_control && !empty($exercise_stat_info['exe_id']) && !empty($clock_expired_time)) {
-    $time_left_check = api_strtotime($clock_expired_time->format('Y-m-d H:i:s'), 'UTC') - time();
+    $time_left_check = api_strtotime($clock_expired_time, 'UTC') - time();
     if ($time_left_check <= 0) {
         $result_url = api_get_path(WEB_CODE_PATH).'exercise/result.php?'
             . api_get_cidreq()
diff --git a/public/main/inc/lib/exercise.lib.php b/public/main/inc/lib/exercise.lib.php
index 218f3fe9f65..c0651077a8a 100644
--- a/public/main/inc/lib/exercise.lib.php
+++ b/public/main/inc/lib/exercise.lib.php
@@ -2030,8 +2030,12 @@ public static function get_session_time_control_key(
             $lp_id,
             $lp_item_id
         );
-        if (isset($_SESSION['expired_time']) && isset($_SESSION['expired_time'][$time_control_key])) {
-            $return_value = $_SESSION['expired_time'][$time_control_key];
+	if (isset($_SESSION['expired_time']) && isset($_SESSION['expired_time'][$time_control_key])) {
+            if ($_SESSION['expired_time'][$time_control_key] instanceof DateTimeInterface) {
+                $return_value = $_SESSION['expired_time'][$time_control_key]->format('Y-m-d H:i:s');
+            } else {
+                $return_value = $_SESSION['expired_time'][$time_control_key];
+            }
         }
 
         return $return_value;