Dust off your copy of Batman: Arkham City (Xbox 360)
and/or Batman: Arkham City (PC)
as tomorrow is St. Roch's Day, which marks another opportunity to pay The Calendar Man a visit in the basement of the Courthouse within the game. Doing so will make a small amount of progress towards one or both of these achievements dependant on the version you own:
If you're not patient enough to wait until midnight tonight, you can forward the time zone on your console to pay the visit that little bit earlier.