… and I want to change it back?

It depends on the operating system.

The latest documentation from Microsoft states


Registry path

Windows XP, Windows Vista, Windows 7, Windows Server 2003, Windows Server 2003 R2, Windows Server 2008, and Windows Server 2008 R2

This entry specifies the maximum offset (in seconds) for which W32Time attempts to adjust the computer clock by using the clock rate. When the offset exceeds this rate, W32Time sets the computer clock directly. The default value for domain members is 300. The default value for stand-alone clients and servers is 1. …

The article goes on to show you, with a formula, how to calculate what will happen if you change your time clock.

How Windows 2000 did it