function currentTime($night = null, $morning = null, $day = null, $evening = null)

{

    $time = (new DateTime)->format('G');

    if ($time >= 0 && $time <= 6) {

        return $night;

    } elseif ($time >= 6 && $time <= 12) {

        return $morning;

    } elseif ($time >= 12 && $time <= 18) {

        return $day;

    } elseif ($time >= 18 && $time <= 23) {

        return $evening;

    }

}



echo currentTime('ночь', 'утро', 'день', 'вечер');