According to 9to5Mac, a number of people have taken to twitter to vent about an issue with the iPhone’s built in alarm clock caused by the switch to the new year. Apparently, if you tried setting your alarm clock for today, it didn’t work.
It appears however, that the issue is only for non recurring times (i.e. every Monday) and the issue seems to fix itself on January 3rd.
If you know someone who has an iPhone, or you have one yourself, don’t use it as your main alarm clock until Monday.