A newly published Apple Support document addresses the issue of iOS 6’s Do Not Disturb mode staying on past its scheduled end time. This issue arose on January 1, 2013.
Apple’s document states: 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.
Apple’s brief document in full is here.
[Thanks to MacDailyNews readers too numerous to mention individually for the heads up.]