Currently Being ModeratedJan 2, 2013 12:13 PM (in response to Moolivia)
It doesn't denote night time hours, its actually a feature.
Thats the Do Not Disturb feature. You can turn it off in Settings > Do Not Disturb. You can also customise it in Settings > Notifications > Do Not Disturb.
Currently Being ModeratedJan 2, 2013 12:17 PM (in response to bbfc)
So that's what it was! Now I feel pretty dumb.
I turned off Do Not Disturb, but it says it's scheduled for 10 PM. I don't remember ever turning it on or scheduling it in the first place; I'll have to fix that.
Currently Being ModeratedJan 5, 2013 11:46 AM (in response to sarir97)
This is a known bug with the Do Not Disturb feature that Apple say will be fixed in a couple of days.
EDIT: This also. http://support.apple.com/kb/TS4510?viewlocale=en_US&locale=en_US