计算php中经过的时间 - 超过24小时

What I am trying to do is add up hours/mins/secs that span over 24 hours, for example:

12:39:25
08:22:10
11:08:50
07:33:05

What I would like it to return is "39:43:30" rather than a date from 1970. Below is the code I'm currently using (note - its from within a class, not just a function).

private function add_time($time1, $time2)
{
$first_exploded = explode(":", $time1);
$second_exploded = explode(":", $time2);
$first_stamp = mktime($first_exploded[0],$first_exploded[1],$first_exploded[2],1,1,1970);
$second_stamp = mktime($second_exploded[0],$second_exploded[1],$second_exploded[2],1,1,1970);
$time_added = $first_stamp + $second_stamp;
$sum_time = date("H:i:s",$time_added);
return $sum_time;
}

Any advise would be much appreciated.

Here's a nice little function that will add up any number of times passed in an array:-

function addTimes(Array $times)
{
    $total = 0;
    foreach($times as $time){
        list($hours, $minutes, $seconds) = explode(':', $time);
        $hour = (int)$hours + ((int)$minutes/60) + ((int)$seconds/3600);
        $total += $hour;
    }
    $h = floor($total);
    $total -= $h;
    $m = floor($total * 60);
    $total -= $m/60;
    $s = floor($total * 3600);
    return "$h:$m:$s";
}

Use it like this:-

$times = array('12:39:25', '08:22:10', '11:08:50', '07:33:05',);
var_dump(addTimes($times));

Output:-

string '39:43:30' (length=8)

Date functions always work around/with day/month/year. What you want is a simple mathematical function, didn't test it but should make it clear.

private function add_time($base, $toadd) {
     $base = explode(':', $base);
     $toadd = explode(':', $toadd);

     $res = array();
     $res[0] = $base[0] + $toadd[0];
     $res[1] = $base[1] + $toadd[1];
     $res[2] = $base[2] + $toadd[2];
     // Seconds
     while($res[2] >= 60) {
         $res[1] += 1;
         $res[2] -= 60;
     }
     // Minutes
     while($res[1] >= 60) {
         $res[0] += 1;
         $res[1] -= 60;
     }
     return implode(':', $res);
}