When you use the Date/Time tool in Control Panel to select a different year, the clock may stop until you click Apply or OK and the clock does not compensate for the length of time it was stopped.
When you use the Date/Time tool to select a different month or date, the time may be decreased by 5-10 seconds.
When you leave your computer on for an extended amount of time, the time may lose from two minutes to an hour per day. IMPORTANT: The CMOS does keep the correct time and if you restart the computer, the Windows clock is updated. Also, if you start your computer in Safe Mode, Windows does not lose time.
How to adjust time via the Internet