Apple has said that the glitch that is affecting the "Do Not Disturb" function in iOS 6 will be fixed by January 7.
On its support forum, Apple has said, “After January 1st, 2013, Do Not Disturb mode stays on past its scheduled end time. Do Not Disturb scheduling feature will resume normal functionality after January 7, 2013. Before this date, you should manually turn the Do Not Disturb feature on or off. To turn off the scheduling feature, tap Settings > Notifications > Do Not Disturb and switch Scheduled to off.”
Complaints started surfacing on Tuesday that the Do Not Disturb feature, which silences calls, alerts, and notifications while enabled stopped working after New Year’s eve. This bug is not restricted to particular countries, as complaints have come from all over the world.
MacRumors forum is flooded with complaints about the Do Not Disturb feature not working. The top complaint reads, “Hello and Happy New Year, I am in Japan so it is 2013, and I am finding that my iOS devices (iPhone 4 and iPad 2) are showing “Do Not Disturb” even though it is outside of the time I set for them. Not sure if this is related to the New Year. Reloading the devices does not help and the software is up-to-date. Anybody else seeing this issue?”
Source: Apple Support Forum