When we in the USA went to Daylight Savings Time a few weeks back, my iPhone 4S (on iOS 5.0.1) did NOT "spring forward." in fact, I moved a different time zone (from Eastern to Central time).
To be on the safe side - i'd have another alarm set ... Just in case.
Of course, by now, you are probably asleep... So I hope it worked out for you.
Marilyn