Get rest time in a week

<?php
getRestTime();

function getRestTime(){
    $TimePlay = getTime();
    $day = $TimePlay[0];
    $hour = $TimePlay[1];
    $minute = $TimePlay[2];
    $second = $TimePlay[3];

    $sumTimePlay = $day*24*60*60 +  $hour*60*60 + $minute*60 + $second;
    $week = 7*24*60*60;

    $sumRestTime = $week - $sumTimePlay;

    $mod = $sumRestTime % (24*60*60);
    $day = ($sumRestTime - $mod) / (24*60*60);

    $rest_time = $sumRestTime - $day * 24*60*60;
    $mod = $rest_time % (60*60);
    $hour = ($rest_time - $mod) / (60*60);

    $rest_time = $rest_time - $hour * 60*60;
    $mod = $rest_time % 60;
    $minute = ($rest_time - $mod) / 60;

    $second = $rest_time - $minute * 60;

    /*
    $original_time_string = "2015-09-20 00:00:00";
    $original_time = convert_datetime($original_time_string);
    $now = time();
    echo "<br>--------------<br>";
    echo $original_time_string;
    echo "<br>";
    echo date('Y-m-d H:i:s', $now);
    echo "<br>";
    echo $day . " " . $hour . " " . $minute . " " . $second;
    */

    return array ($day, $hour, $minute, $second);
}

function getTime(){
    $original_time_string = "2015-09-20 00:00:00";
    $original_time = convert_datetime($original_time_string);
    $now = time();

    $rest_time = $now - $original_time;
    $mod = $rest_time % (24*60*60);
    $day = ($rest_time - $mod) / (24*60*60);

    $day2 = $day % 7;

    $rest_time = $rest_time - $day * 24*60*60;
    $mod = $rest_time % (60*60);
    $hour = ($rest_time - $mod) / (60*60);

    $rest_time = $rest_time - $hour * 60*60;
    $mod = $rest_time % 60;
    $minute = ($rest_time - $mod) / 60;

    $second = $rest_time - $minute * 60;

    /*
    echo $original_time_string;
    echo "<br>";
    echo date('Y-m-d H:i:s', $now);
    echo "<br>";
    echo $day2 . " " . $hour . " " . $minute . " " . $second;
    */

    return array ($day2, $hour, $minute, $second);

}

function convert_datetime($str) {
    list($date, $time) = explode(' ', $str);
    list($year, $month, $day) = explode('-', $date);
    list($hour, $minute, $second) = explode(':', $time);
    $timestamp = mktime($hour, $minute, $second, $month, $day, $year);
    return $timestamp;
}

?>