PHPは日付の差を計算します

date_default_timezone_set("アジア/カルカッタ");

function dt_differ($start, $end){
 $start = date("G:i:s:m:d:Y", strtotime($start ));
 $date1=explode(":", $start);

 $end = date("G:i:s:m:d:Y", strtotime($end));
 $date2=explode (":", $end);

 $starttime = mktime(date($date1[0]),date($date1[1]),date($date1[2]),
 date($date1[3] ]),date($date1[4]),date($date1[5]));
 $endtime = mktime(date($date2[0]),date($date2[1]),date($date2 [2]),
 date($date2[3]),date($date2[4]),date($date2[5]));

 $seconds_dif = $starttime-$endtime;

 return $seconds_dif ;
}

PHP