- date: documentation ( source)
- strtotime: documentation ( source)
<?php
$cut = 3600;
$date_start = strtotime("2017-11-02 02:19:59");
$date_end = strtotime("2017-11-02 03:32:06");
$total = ($date_end - $date_start) - $cut;
if($total < 0){
echo '0';
}else{
echo date("H:i:s", $total);
}