Originally Posted by Atomic Clock Sync v3.0

IMPORTANT NOTE: You must have the correct time zone selected on your computer AND have the correct daylight saving time rules in place in your operating system in order to have the Internet Time synchronize process work properly. If the dates for Daylight Saving Time (DST) changed recently in your area, you must update your operating system with the new rules. Microsoft releases patches when necessary for newer versions of Windows, but with older versions, you may have to update the registry yourself or find a third-party tool to do it.