TimeHelper::getUtcTimestampForUserTime

public function getUtcTimestampForUserTime($userId, $daySeconds, $date = null)
{
	$timeZone = $this->getUserTimezone($userId);
	if (!($timeZone instanceof DateTimeZone))
	{
		return null;
	}
	if ($date === null)
	{
		$date = $this->getUserDateTimeNow($userId);
	}
	$dateFormatted = $date->format('Y-m-d');

	$seconds = str_pad($this->getSeconds($daySeconds), 2, '0', STR_PAD_LEFT);
	$dateTime = DateTime::createFromFormat(
		'Y-m-d H:i:s',
		$dateFormatted . ' ' . $this->convertSecondsToHoursMinutes($daySeconds) . ':' . $seconds,
		$timeZone
	);
	if (!$dateTime)
	{
		return null;
	}
	return $dateTime->getTimestamp();
}