Difference between 2 time entries

Morning all, I am looking to get the differnce in hours / minutes between 2 values. Currently I have 2 time entries being retruned from mysql, one which is a start time and the other which is a finish time. So $start = '13:12:17'; $finish = '23:12:17'; How would one get the differnce between these 2 times?? I have looked at using the following but am not to sure.... function timeDiff($firstTime,$lastTime) { // convert to unix timestamps $firstTime=strtotime($firstTime); $lastTime=strtotime($lastTime); // perform subtraction to get the difference (in seconds) between times $timeDiff=$lastTime-$firstTime; // return the difference return $timeDiff; } //Usage : echo timeDiff("$start","$finish"); Thanks Chris