datetime - How to calculate the time consumed from start time to end time in php -

i want perfect time consumed or total time start time end time:
code:

   $start_time =  $this->input->post('start_time');    $end_time =  $this->input->post('end_time');      $t1  = strtotime($start_time);    $t2 = strtotime($end_time);    $differenceinseconds = $t2 - $t1;    $differenceinhours = $differenceinseconds / 3600;     if($differenceinhours<0) {      $differenceinhours += 24;      } 

in code above if $start_time = 11:00:00 pm , $end_date =11:30:00 gives me output of 0.5 instead of 30minutes. there appropriate way that?
if the:

  $start_time  = '01:00:00 pm';   $end_time = '01:25:00 pm';    $total = '25:00'; // 25 minutes 

or:

  $start_time  = '11:00:00 pm';   $end_time = '11:00:25 pm';    $total = '00:00:25'; // 25seconds 

regards!

try diff function

<?php echo date_create('03:00:00 pm')->diff(date_create('03:25:00 pm'))->format('%h:%i:%s'); ?> 

output

---

00:25:00