I have clocks that are "atomic" clocks and syncronized by NBS (via radio signals.)
At 11:20 am I tried checking in for a flight tomorrow at 11:20 am and got the a message that the system could not check me in and I would have to see an agent. [The inability to ci is sometimes because of SSSS.] A few seconds later I was able to ci and print my bp. aa's clocks may not be 100% in sych with NBS.
[I've been told by an aangel at an ac, that she knew two fliers who frequently flew on the same flight (both exps) and each one tried to check in before the other (from different locations)--frequently the time difference was only a few seconds--but the first one got the upgrade in some instances.]