- date_default_timezone_set: documentation ( source)
- date: documentation ( source)
- strtotime: documentation ( source)
<?php
date_default_timezone_set('America/New_York');
$a = strtotime('08:00');
$b = strtotime('03:00');
echo $a."\r\n"; echo $b;
$c = $a - $b;
$d = date('H:i:s',18000);
echo "\r\n".$c;
echo "\r\n".$d;