<?php
$t1= '0:2:00';
$t2= '0:0:01';
$a1 = explode(":",$t1);
$a2 = explode(":",$t2);
$time1 = (($a1[0]*60*60)+($a1[1]*60)+($a1[2]));
$time2 = (($a2[0]*60*60)+($a2[1]*60)+($a2[2]));
$diff = abs($time1-$time2);
$hours = floor($diff/(60*60));
$mins = floor(($diff-($hours*60*60))/(60));
$secs = floor(($diff-(($hours*60*60)+($mins*60))));
$result = $hours.":".$mins.":".$secs;
echo $result;