- date_default_timezone_set: documentation ( source)
- strtotime: documentation ( source)
<?php
date_default_timezone_set("America/Los_Angeles");
$startDate = "04/04/2016 7:00 AM America/New_York";
$ts = strtotime($startDate);
$dt = new DateTime();
$dt->setTimestamp($ts);
echo $dt->format("Y-m-d H:i:s\Z");