You might think that AD time sync in your organisation is something that just works out of the box but Sander Berkouwer has just done a post about what you need to do to setup time sync for Windows Server 2008 & R2. Apparently the default time sync server for Windows Server 2003 (time.windows.com) no long works so you need to make sure that you DC are configured with a valid time source.
Check out the whole article here The things that are better left unspoken : Active Directory Time Sync (broken by default)
Tip: One of the steps in the article is to configure the time server using the “w32tim” command on your PDC emulator. You can do this via Group Policy Preferences using the scheduled task option and then use Item-Level Targeting to only apply the command to the computer name of your PDC Emulator. By scheduling this command on a regular basis you can ensure that the time zone list of the server gets refreshed to the proper values periodically.