timestamp difference in day hours php code example

Example 1: difference between two timestamps php

$datetime1 = new DateTime('2016-11-30 03:55:06');//start time
$datetime2 = new DateTime('2016-11-30 11:55:06');//end time
$interval = $datetime1->diff($datetime2);
echo $interval->format('%Y years %m months %d days %H hours %i minutes %s seconds');//00 years 0 months 0 days 08 hours 0 minutes 0 seconds

Example 2: difference of two dates in seconds php

$timeFirst  = strtotime('2011-05-12 18:20:20');
$timeSecond = strtotime('2011-05-13 18:20:20');
$differenceInSeconds = $timeSecond - $timeFirst;