diff --git a/mod/assign/classes/output/user_submission_actionmenu.php b/mod/assign/classes/output/user_submission_actionmenu.php
index 4c8b121102313..6cbfddc8617e9 100644
--- a/mod/assign/classes/output/user_submission_actionmenu.php
+++ b/mod/assign/classes/output/user_submission_actionmenu.php
@@ -131,7 +131,8 @@ public function export_for_template(\renderer_base $output): array {
             }
             if ($status === ASSIGN_SUBMISSION_STATUS_NEW) {
 
-                if ($this->timelimit && empty($this->submission->timestarted)) {
+                $timelimitenabled = get_config('assign', 'enabletimelimit');
+                if ($timelimitenabled && $this->timelimit && empty($this->submission->timestarted)) {
                     $confirmation = new \confirm_action(
                         get_string('confirmstart', 'assign', format_time($this->timelimit)),
                         null,
diff --git a/mod/assign/override_form.php b/mod/assign/override_form.php
index e30e4d4234b31..8f5f7cf49019b 100644
--- a/mod/assign/override_form.php
+++ b/mod/assign/override_form.php
@@ -263,9 +263,12 @@ protected function definition() {
         }
 
         // Time limit.
-        $mform->addElement('duration', 'timelimit',
-            get_string('timelimit', 'assign'), array('optional' => true));
-        $mform->setDefault('timelimit', $assigninstance->timelimit);
+        $timelimitenabled = get_config('assign', 'enabletimelimit');
+        if ($timelimitenabled) {
+            $mform->addElement('duration', 'timelimit',
+                get_string('timelimit', 'assign'), array('optional' => true));
+            $mform->setDefault('timelimit', $assigninstance->timelimit);
+        }
 
         // Submit buttons.
         $mform->addElement('submit', 'resetbutton',
@@ -344,7 +347,7 @@ public function validation($data, $files) {
         $changed = false;
         $keys = array('duedate', 'cutoffdate', 'allowsubmissionsfromdate', 'timelimit');
         foreach ($keys as $key) {
-            if ($data[$key] != $assigninstance->{$key}) {
+            if (isset($data[$key]) && $data[$key] != $assigninstance->{$key}) {
                 $changed = true;
                 break;
             }
diff --git a/mod/assign/overrideedit.php b/mod/assign/overrideedit.php
index 76fb11b2f827a..88f38217baf8d 100644
--- a/mod/assign/overrideedit.php
+++ b/mod/assign/overrideedit.php
@@ -144,7 +144,7 @@
 
     // Replace unchanged values with null.
     foreach ($keys as $key) {
-        if (($fromform->{$key} == $assigninstance->{$key})) {
+        if (!isset($fromform->{$key}) || $fromform->{$key} == $assigninstance->{$key}) {
             $fromform->{$key} = null;
         }
     }
diff --git a/mod/assign/overrides.php b/mod/assign/overrides.php
index dd65575ebae20..e41efdb992cfa 100644
--- a/mod/assign/overrides.php
+++ b/mod/assign/overrides.php
@@ -211,7 +211,8 @@
     }
 
     // Format timelimit.
-    if (isset($override->timelimit)) {
+    $timelimitenabled = get_config('assign', 'enabletimelimit');
+    if ($timelimitenabled && isset($override->timelimit)) {
         $fields[] = get_string('timelimit', 'assign');
         $values[] = $override->timelimit > 0 ? format_time($override->timelimit) : get_string('none', 'assign');
     }