I'm not sure how Windows 8 does it, however my Windows 7 Pro: start --> run --> services --> find Windows Time. I think setting it manual or disable might accomplish what you want.
well-balanced, well-configured mult-layered defense is best
Other Info
From MS-DOS 3.3, MS-DOS 6.22, from Windows 3.1 to WFW 3.11 to Windows 95-98SE, now to Windows 7 Pro.
Security for now: Windows 7 Firewall, Emsisoft AM, MSE [scan-only], SpywareBlaster, Ruiware/BillP combine
Personally..... I never found Windows Time to be reliable, so....
I just disable it and I use an "Atom Time" or "Chronograph" program to sync my system clock to the Bureau of Standards.