protected function validateTimestamp(&$value, array $field, Validation $validation) {
        $validType = true;
        if (is_numeric($value)) {
            $value = (int)$value;
        } elseif (is_string($value) && $ts = strtotime($value)) {
            $value = $ts;
        } else {
            $validType = false;
        }
        return $validType;
    }