[Fighter]

имхо, для эмулятора PDA первого домена в лесу это уже external time provider
How Windows Time Service Works
впрочем, мне понравился вариант в статье Mitch`a Tulloch`a
Configuring the Windows Time Service

W32Time synchronizes clocks within a forest using a time hierarchy that begins with the PDC Emulator in the forest root domain, which is considered the stratum 2 time source for the forest. This domain controller can have its own clock controlled several ways: - By synching to a reliable time server on the Internet. - By synching to an locally-connected hardware time source such as an atomic clock. - By relying on its own internal CMOS clock for reliable time.