Re: Every user?
Twilight Zone music..
Imagine if you will, multiple active directory domains, all with their own idea of where to get time. Mix in some none AD legacy machines where some noob had just clicked through windows setup leaving it set to US time. Then add in a concerted effort to sync these up - by pointing them all to a time server on a network switch which itself was firewalled off from the outside world. Do it slightly different on each AD so as some fail to talk to the switch ntp at all and never check. Finally, refuse to allow downtime for the legacy 24/7 unix machines to install ntp because if it screwed up so bad for windoze then it must be impossible to do it without rebooting unix. Couple this with people logging in remotely and you get a situation where time can indeed go backward and not just on the GMT/BST dates either.
If only the raspberry pi was a thing back then. There'd be one hidden in a rack somewhere dishing up time properly and all the unix boxes would be pointing to it!