I use a freeware SNTP app which gets time from a time server every hour. Depending on the PC, the time can be off by a second or so before it's adjusted.
Look for cmdtime (the copy I got was from [link|http://www.softshape.com/download/#freeware|softshape.com] for Win32) or something similar. Lots of similar things for *nix and OS/2.
If you need better resolution, you might need something else...
HTH.
Cheers,
Scott.