In OS X make sure you go to System Preferences->Date & Time and use a time server to automatically. Plus tell us what version of OS X you are running and what version of windows are you using in Boot Camp.
Windows and OS X use different bases to compute local time.
Make sure that the time zone is set properly for your local time zone.
Also, make sure the network time settings are set for that same time zone in the Windows control panel, and that is also set to use the network time.