Util::getDateTimestamp

static function getDateTimestamp(?string $dateFrom, ?string $timezone): ?int
{
	if (!$dateFrom || !$timezone)
	{
		return null;
	}

	$date =  new BitrixCalendarCoreBaseDate(
		Util::getDateObject(
			$dateFrom,
			false,
			$timezone
		)
	);

	return $date->getTimestamp();
}