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$date = new \DateTime();
$date->setTimezone(new \DateTimeZone('+0800')); //GMT
echo $date->format('Y-m-d H:i:s');
// 2020-11-20 15:23:49
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$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