- strtotime: documentation ( source)
<?php
$timezone = new DateTimeZone( 'UTC' );
$datetime = new DateTime();
$datetime->setTimezone( $timezone );
$datetime->setTimestamp( strtotime( '2013-02-13 13:59:27' ) );
echo $datetime->format( 'Y-m-d H:i:s' ); //2013-02-13 12:59:27