protected function getDateTimestamp($value)
    {
        if ($value instanceof DateTimeInterface) {
            return $value->getTimestamp();
        }

        if ($this->isTestingRelativeDateTime($value)) {
            $date = $this->getDateTime($value);

            if (! is_null($date)) {
                return $date->getTimestamp();
            }
        }

        return strtotime($value);
    }