Apple has released a support document highlighting the problem of iPhone alarms setting of one hour late, as the US switch from Daylight Savings Time tonight.
The Apple Knowledge Base article 'iOS 4.1: Repeating alarms may trigger incorrectly before or after DST change,' 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.
This isn't the first time that the switch has caused problems for iPhone users. At the end of September and the beginning of October, the change caused alarms in New Zealand and Australia to go off one hour early.
Apple devices affected by the bug are iPod touch (4th generation), iPod touch (3rd generation), iPhone 3G, iPhone 4, iPhone 3GS and the iPod touch (2nd generation).