How to access date value from a datelist form element for validation?
Yes, to compare the date it's better to use the unix timestamp. You can get it by using the method getTimeStamp() and compare it to the current date:

      $value = $form_state-&gt;getValue('date_field');
      if ($value-&gt;getTimeStamp() &gt; REQUEST_TIME) {
        drupal_set_message('Time is in the future');
      }