[Update, 1/1/11 at 12:41 p.m. PT: Apple spokesperson Natalie Harrison confirmed to Macworld that Apple is aware of the problem. "We're aware of an issue related to non repeating alarms set for January 1 or 2," Harrison said. "Customers can set recurring alarms for those dates and all alarms will work properly beginning January 3."]
Users in 2011 have sent a message back to those of us in 2010: one-time iOS alarms don’t seem to be working right in the future.
I was able to confirm this after a couple of false starts. For the bug to show itself, your iOS device must actually tick over from 11:59 p.m. on December 31, 2010 to 12:00 a.m. on January 1, 2011. (Good news for time travelers!)
Once you’ve passed that special minute and your iPhone has shot off its virtual confetti cannon, the bug occurs: one-time alarms set for 12:01 a.m., for example, won’t go off. (I was able to set a recurring event for every Saturday at 12:03 a.m., and that one went off.)
The workaround for this is easy: set your alarm for New Year’s Day to be an “every Saturday” alarm.
According to a 9to5mac report, this bug lasts through January 3, then fixes itself. I haven’t had a chance to test that claim.