How Things Tick with the Windows Time Synchronization Service
At system startup, a Windows 2000 client machine participating in a domain contacts the domain controller to be authenticated to the domain. Getting your clock synched is an active process: The client machine makes a request to the domain controller for time synchronization information.
During the authentication process, the client attempts to adjust its own system clock based on the clock of the server (that is, the domain controller) with which it's trying to authenticate. This adjustment is known as time convergence:
If the client's clock is ahead of the domain controller's clock (within three minutes), the client gradually slows its own clock long enough to bring the client and the domain controller into sync. If the client clock is ahead of the domain's controller's clock by more than three minutes, an immediate synchronization is forced.
If the client clock is behind that of the domain controller, the client immediately matches its own clock time to reflect that of the domain controller.
After the logon-based synchronization operation, the time service attempts to synchronize with the designated time server every 45 minutes until the clock has synchronized three times. If this tactic is successful, the Windows 2000 client continues periodically trying to verify its clock, to make sure that the clock is in sync with the time server. This check occurs every eight hours, by default.