public function validTimeStr ( $time ) {
        if ($time === '0000-00-00 00:00:00') {
            return true;
        }

        if ($this->fitNonExistingDates && $this->isNonExistingTimeString( $time )) {
            $time = $this->getPossibleDateString( $time );
        }

        return (is_string( $time ) && strlen( $time ) == 19 && $time == date( 'Y-m-d H:i:s',
                                                                              strtotime( $time ) ));
    }