Today is Halloween Thanksgiving Christmas New Year's Day Valentine's Day. So if you're playing Batman: Arkham City and you don't believe in cheating by changing your system's internal clock, go talk to the Calendar Man today.

He's in the basement of the courthouse near the top of the map (the courthouse where you first encounter Two-Face and Catwoman). Use the back entrance and head downstairs. He has something to tell you.

He'll want to chat again on Thanksgiving, November 24.
He''ll want to chat again on Christmas, December 25.
He''ll want to chat again on New Year's Day, January 1.
He''ll want to chat again on Valentine's Day, February 14.
He'll want to chat again on St. Patrick's Day, March 17.