To get the difference between two time strings use this code
<?php 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("2002-04-16 10:00:00","2002-03-16 18:56:32"); ?>