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w32time is not NTP. If you had NTP running on the box we would be able
help you. You need to ask Microsoft about this.
If your clock is drifting that much either it's not able to connect to
a remote service, and your event log would tell you that. You did look
at the event log, right?
Also if the system is heavily loaded you could be losing interrupts but
you have told us nothing about the system.
Install NTP, disable w32time and then we can discuss it.