How to set time server for Windows server 2008, SBS2011 & 2012
Often our server and workstation doesn’t have the right time. Best way is to change the NTP time server on the Domain Controller. Here’s how to change your time server from what ever it is now to another NTP server.
Another good source and more details can be found here:
http://www.thirdtier.net/2011/02/how-to-set-an-ntp-time-server-in-windows-2008-sbs-2008-and-sbs-2011/