- timezone_offset_get: documentation ( source)
<?php
$original_timezone = new DateTimeZone('UTC');
$datetime = new DateTime('06-01-2016 19:00 UTC', $original_timezone);
$target_timezone = new DateTimeZone('EDT');
$datetime->setTimeZone($target_timezone);
$triggerOn = $datetime->format('Y-m-d h:i:s T P');
echo $triggerOn;
echo timezone_offset_get($target_timezone,$triggerOn);