code: public function updateTimeReference(AssessmentTestSession $session, \DateTime $time = null) {
          if ($time === null) {
              $time = new \DateTime('now', new \DateTimeZone('UTC'));
          }
  
          $itemSession = $session->getCurrentAssessmentItemSession();
  
          if ($itemSession) {
              $itemSession->setTimeReference($time);
              $session->updateDuration();
          }
      }
docs: Set time reference of current assessment item session to <i>now</i> instead of time of last update.
  This ensures that time when delivery execution was paused will not be taken in account.
  Make sure that method invoked right after retrieving assessment test session
  and before the first AssessmentTestSession::updateDuration method call
  @param AssessmentTestSession $session
  @param \DateTime|null $time Time to be specified. Current time by default. Make sure that $time has UTC timezone.