protected function get_either_description($not, $standalone) {
        $direction = $this->get_logical_direction($not);
        $midnight = self::is_midnight($this->time);
        $midnighttag = $midnight ? '_date' : '';
        $satag = $standalone ? 'short_' : 'full_';
        switch ($direction) {
            case self::DIRECTION_FROM:
                return get_string($satag . 'from' . $midnighttag, 'availability_date',
                        self::show_time($this->time, $midnight, false));
            case self::DIRECTION_UNTIL:
                return get_string($satag . 'until' . $midnighttag, 'availability_date',
                        self::show_time($this->time, $midnight, true));
        }
    }