I know that there was a glitch (I think for spring ahead) where you had to turn the alarm off and then reset it for the time change. Maybe you needed to do that? Turn the alarm off and then back on....instead of just keeping it on it's regular schedule.
If the alarm went off at the same time it would have without the time change...it should have gone off early. Because 6 became 5 today. Which is what happened with mine. Mine also switched time on me. One minute it was the correct time for today and the next minute it was the correct time if the time hadn't changed. I have a poor 3G signal here at the house (1-2) bars and I wonder if the poor connection to the network wasn't to blame. At any rate a hard reset seems to have sorted it out. I'll just have to make sure to set my actual alarm clock for tomorrow so I'm not late for work.