We have just installed a new server and Windows Server 2010 R2 I believe. My Windows 7 workstations all seem to key off the time on the server and it keeps following behind about 10 minutes in two or three days. Can't I assume my CMOS battery would be new and therefore not the problem?
Never assume your hardware will keep accurate time. Despite the tolerances of the manufacturing process, internal clocks are wonky. Heck, I've seen cases where line voltage differentials can cause time skew. Use NTP.