Windows XP Time Service and Polling

I am working with a Time Server on multiple networks that need to be synchronized. The server has 3 individual ports distributing amongst them. It seems that due to the time interval that Windows is polling, the networks are breaking time. They seem to be off about 9 to 10 seconds after about a week of running. I have found that the following can be altered for time intervals, but need to know any pitfalls that may come along with it:

regedit, hkey_local_machine, system, CurrentControlSet, services, w32time, TimeProviders, NTPCliet, SpecialPollInterval.

I’d like to poll time approximately every 4 to 8 hours. Any suggestions, Please advise. Thanks!