How to convert between time zones in PHP using the DateTime class?

What you’re looking for is this:

$triggerOn = '04/01/2013 03:08 PM';
$user_tz = 'America/Los_Angeles';

echo $triggerOn; // echoes 04/01/2013 03:08 PM

$schedule_date = new DateTime($triggerOn, new DateTimeZone($user_tz) );
$schedule_date->setTimeZone(new DateTimeZone('UTC'));
$triggerOn =  $schedule_date->format('Y-m-d H:i:s');

echo $triggerOn; // echoes 2013-04-01 22:08:00