code: public function getReviewDate(SiteTree $page = null)
      {
          if ($page === null) {
              $page = $this->owner;
          }
  
          if ($page->obj('NextReviewDate')->exists()) {
              return $page->obj('NextReviewDate');
          }
  
          $options = $this->owner->getOptions();
  
          if (!$options) {
              return false;
          }
  
          if (!$options->ReviewPeriodDays) {
              return false;
          }
  
          // Failover to check on ReviewPeriodDays + LastEdited
          $nextReviewUnixSec = strtotime(' + ' . $options->ReviewPeriodDays . ' days', DBDatetime::now()->getTimestamp());
          $date = DBDate::create('NextReviewDate');
          $date->setValue($nextReviewUnixSec);
          return $date;
      }
docs: Returns false if the content review have disabled.
  
  @param SiteTree $page
  
  @return bool|DBDate