- date_default_timezone_set: documentation ( source)
<?php
date_default_timezone_set('America/New_York');
$dtLastUpdate = DateTime::createFromFormat('Ymd', '20140704');
$dtLastUpdate->format('Ymd');
$now = new DateTime();
$now->format('Ymd');
$dDiff = $dtLastUpdate->diff($now);
echo $dDiff;