protected function computeRollover($currentTime)
    {
        if ($this->when == 'MIDNIGHT') {
            return strtotime("midnight + 1 day", $currentTime);
        }

        if (substr($this->when, 0, 1) == 'W') {
            return strtotime(
                "next " . self::$dayNames[$this->dayOfWeek],
                $currentTime
            );
        }

        return $currentTime + $this->interval;
    }