src/Extensions/SiteTreeContentReview.php
public function advanceReviewDate()
    {
        $nextDateTimestamp = false;
        $options = $this->getOptions();

        if ($options && $options->ReviewPeriodDays) {
            $nextDateTimestamp = strtotime(
                ' + ' . $options->ReviewPeriodDays . ' days',
                DBDatetime::now()->getTimestamp()
            );

            $this->owner->NextReviewDate = DBDate::create()->setValue($nextDateTimestamp)->Format(DBDate::ISO_DATE);
            $this->owner->write();
        }

        return (bool)$nextDateTimestamp;
    }
public function advanceReviewDate()
    {
        $nextDateTimestamp = false;
        $options = $this->getOptions();

        if ($options && $options->ReviewPeriodDays) {
            $nextDateTimestamp = strtotime(
                ' + ' . $options->ReviewPeriodDays . ' days',
                DBDatetime::now()->getTimestamp()
            );

            $this->owner->NextReviewDate = DBDate::create()->setValue($nextDateTimestamp)->Format(DBDate::ISO_DATE);
            $this->owner->write();
        }

        return (bool)$nextDateTimestamp;
    }
Advance review date to the next date based on review period or set it to null
if there is no schedule. Returns true if date was required and false is content
review is 'off'.

@return bool