Timestamp of a time in a particular timezone

time.php

<?php

$datetimezone_object = new DateTimeZone('Pacific/Nauru'); // new DateTimeZone('PST');
$date = DateTime::createFromFormat( 'Y-m-d H:i:s', '2014-04-14 05:00:00', $datetimezone_object );
echo $date->getTimestamp();