There have been a number of reports about a bug in iOS 6 over the last few days, related to Apple’s ‘Do Not Disturb’ feature in iOS 6, the problem with the feature is that it has not turned itself off when it was set to do so.
Apple has now released a support document relating to the bug, and suggested that the issue will fix itself manually by the 7th of January, in the meantime you will have to manually turn the feature off yourself.
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.
You can find out more information about the issue with the Do Not Disturb feature on iOS 6 devices over at Apple.