For reasons that are probably best ignored, the recent switch in daylight savings time seems to have freaked out the iPhone alarm settings. Some alarms, according to reports, have gone off an hour later than expected.
Although some alarms (such as “Every day” and “No repeat”) seem to be unaffected, it ppears that deleting and re-adding the alarm won’t fix it either. If your alarm is set for “weekdays” (for example) then you’ll probably just have to set it to go off an hour earlier than you actually need. Fail.
Link – ZDNet