I always have my alarm set for 8:00 AM, but I've seen it go off at random time on more than one occasion, see attached screenshots (look at the clock in the top-right, which is correct). Not sure if I can provide any other useful info, this is completly random, and has happened like twice or thrice in the past two months (not saying it did not happen before, I simply was not using a FxOS phone before).