On any directory-based network, keeping accurate time is critical to running an efficient network and preventing replication problems. The best way to keep the time accurate in your environment is to synchronize the server clock with an outside, reliable time source, such as the National Institute of Standards and Technology (NIST).
Here's how to synchronize your Windows Server 2003 clock with an outside time source:
It's also important to have the correct time zone set on the server and to properly indicate whether your regional area observes daylight savings time. Select this information from the Time Zone tab in Date And Time Properties.
In addition, make sure that all of your clients' time properties are configured properly.