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.
"Siri, remind me to toggle Do Not Disturb"
(Because I'll probably forget to do so, only to be sorry later.)
The second bit of follow-up to this is that I misspoke yesterday when I updated my original post, saying that the bug had apparently been squashed. It hasn't. I noticed the little crescent moon icon in the status bar when I got up this morning a little after 8. My apologies.