MacOS assumes that your machine time is GMT. Windows assumes that your machine time is correct for your time zone. So each time you switch operating systems the time is wrong in one of the systems. The fix is to tell Windows that your machine time is GMT (universal time). Here is the fix:
Boot up your bootcamp partition and logon to your Windows installation
Open Regedit with administrative rights
Create a new DWORD string value called RealTimeIsUniversal in: HKEYLOCALMACHINE > SYSTEM > CurrentControlSet > Control > TimeZoneInformation