<?php
$one = new DateTime('2012-01-24 13:00');
$two = new DateTime('2012-01-24 06:00');
$three = new DateTime('2012-01-24 08:42');
$four = new DateTime('2012-01-24 12:00');
$five = new DateTime('2012-01-24 06:33');
$array = array($one, $two, $three, $four, $five);
foreach($array as $a){
$a->modify("-7 hours");
echo $a->format('Y-m-d H:i') . "\n";
}