- date_diff: documentation ( source)
- date: documentation ( source)
- strtotime: documentation ( source)
<?php
$hour24_seconds = 60*24*60;
$checkout_time = date("Y-m-d H:i:s");
echo $checkout_time.">>>>>>".date("Y-m-d H:i:s", strtotime($checkout_time) + $hour24_seconds);
echo ">>>>>>>>>>>>>>>>>>>>>>>>>>".date_diff("2012-02-02", "2012-02-05");