- mktime: documentation ( source)
- date_default_timezone_set: documentation ( source)
- strtotime: documentation ( source)
- date_default_timezone_get: documentation ( source)
<?php
echo date_default_timezone_get() . "\n";
date_default_timezone_set('UTC');
$timestamp = mktime(0,0,0,11,1,2014);
echo strtotime('4 thursdays', $timestamp) . "\n";
echo strtotime('first thursday + 3 weeks', $timestamp) . "\n";