Apple has acknowledge the Do Not Disturb bug that has plagued some iOS users since January 1st and revealed that the feature won't work properly until January 7th.
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.
Read More [via @EvilPenguin_]