sumHours.php

<?php

function somar_horas($time1, $time2) {
    $times = array($time1, $time2);
    $seconds = 0;
    foreach ($times as $time)
    {
      list($hour,$minute,$second) = explode(':', $time);
      $seconds += $hour*3600;
      $seconds += $minute*60;
      $seconds += $second;
    }
    $hours = floor($seconds/3600);
    $seconds -= $hours*3600;
    $minutes  = floor($seconds/60);
    $seconds -= $minutes*60;
    if($seconds < 9)
    {
    $seconds = "0".$seconds;
    }
    if($minutes < 9)
    {
    $minutes = "0".$minutes;
    }
      if($hours < 9)
    {
    $hours = "0".$hours;
    }
    $saida = "{$hours}:{$minutes}:{$seconds}";
    return $saida;
}