CTimeZone::GetOffset

static function GetOffset($USER_ID = null, $forced = false)
{
	global $USER;

	if ($forced)
	{
		if (!self::OptionEnabled())
		{
			return 0;
		}
	}
	else
	{
		if (!self::Enabled())
		{
			return 0;
		}
	}

	try //possible DateTimeZone incorrect timezone
	{
		$timeZone = '';

		if ($USER_ID !== null)
		{
			$dbUser = CUser::GetList('id', 'asc', ['ID_EQUAL_EXACT' => $USER_ID], ['FIELDS' => ['AUTO_TIME_ZONE', 'TIME_ZONE', 'TIME_ZONE_OFFSET']]);
			if (($arUser = $dbUser->Fetch()))
			{
				if (self::IsAutoTimeZone(trim($arUser["AUTO_TIME_ZONE"])))
				{
					// can't detect auto timezone for a non-current user, return actual offset from the DB
					return intval($arUser["TIME_ZONE_OFFSET"]);
				}
				$timeZone = $arUser["TIME_ZONE"];
			}
		}
		elseif (is_object($USER))
		{
			// current user
			$autoTimeZone = $USER->GetParam("AUTO_TIME_ZONE") ?: '';
			if (self::IsAutoTimeZone(trim($autoTimeZone)))
			{
				if (($cookie = static::getTzCookie()) !== null)
				{
					// auto time zone from the cookie
					$timeZone = $cookie;
				}
				elseif (($cookie = static::GetCookieValue()) !== null)
				{
					//auto time offset from old cookie - deprecated
					$localOffset = (new DateTime())->getOffset();
					$userOffset = -($cookie) * 60;

					return $userOffset - $localOffset;
				}
			}
			else
			{
				// user set time zone manually
				$timeZone = $USER->GetParam("TIME_ZONE");
			}
		}

		if ($timeZone == '')
		{
			//default server time zone
			$timeZone = COption::GetOptionString("main", "default_time_zone", "");
		}

		if ($timeZone != '')
		{
			$localOffset = (new DateTime())->getOffset();

			$userTime = new DateTime('now', new DateTimeZone($timeZone));
			$userOffset = $userTime->getOffset();

			return $userOffset - $localOffset;
		}
	}
	catch (Throwable $e)
	{
	}

	return 0;
}