ShackNews reports that the Peggle Nights DLC will arrive on XBLA this Wednesday, November 18. The DLC is a $5 addition to XBLA Peggle, adding sixty-something levels to the game classified in several countries as a controlled substance.
Double-checking with Peggle developer PopCap, the company hasn't officially announced the date in a release and is optimistic that Nights will be available this Wednesday. Checking with Microsoft, the company is "looking into it." So, yeah, there's no reason to doubt anyone, but there doesn't seem to be an affirmation of Peggle Nights' release this week.