I always though advent calendars were missing an easy trick by not including something on the 25th. I understand that advents are leading up to the day, but who wouldn't want an extra day of awesome stuff. Especially beer.
Totally break all the rules and make your advent calendar as long as you want. Do it, the recipient is sure to thank you. I put my 25th day on the end of one of my rows and glued it in place. Then, the entire matrix was bound in duct tape as an extra measure to ensure it all stays together.