the computer is on a lan, but there's no internet access?

You know, you can setup one or more of the computers on the lan to be an ntp (network time protocol) server. I think you can even configure it so it will broadcast the time of day.

Again, I don't remember how to do it, it's somewhere in the management console in Windows IIRC. (just google windows ntp server) It works better if that computer can access a better time source, but if it can't it just uses it's own idea of the time of day, which can still drift. But on a LAN the important thing is generally that all the computers have the same idea of the current time.

All of this is easier to do in linux or pretty much any unix variant.