Apple Says 'Do Not Disturb' Bug to Resolve Itself on Monday, January 7th
Apple reports in a support article that Do Not Disturb scheduling will begin working properly again after January 7, 2013.
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.