algo asi
Código PHP:
<?php
function sumTime(){
$i = 0;
foreach (func_get_args() as $time){
sscanf($time, '%d:%d:%d', $hour, $min, $sec);
$i += $hour * 60 + $min + $sec;
}
if ($h = floor($i / 60)){
$i %= 60;
}
return sprintf('%02d:%02d:%02d', $h, $i, $s);//= echo date("H:i:s");
}
//Como usar
$tm = '20:00:00';
$ex = '10:00:00';
echo sumTime($tm, $ex);//=30:00:00
?>