The Apple Knowledge Base article ',' offers the following advice.

In some regions, shortly before or after the daylight saving time (DST) change, repeating alarms created in the Clock app may work incorrectly.

To resolve this behaviour for existing alarms, set the repeat interval to Never. You will need to reset these alarms for each day you need them. After November 7th, 2010, you can set your alarms to repeat again.

Apple adds the support document will be updated as more information becomes available.

Apple users suffered similar problems across Europe last weekend with many waking late for work on Monday due to the time change and the end of BST in the UK.