Woohoooo! It's the Ideal Bookshelf Holiday Advent Calendar! Every day from December 1st through 12th there will be some sort of crazy surprise going on here. For instance, when you return to this page on Day 4 of the advent (i.e., December 4th), instead of a red box with a white 4 in it, there will be a listing for the "Thing of the Day", whatever that might be. On Day 5, that door will be closed again, but the door with the 5 on it will be open instead. Easy, right?
Each "day" starts at 12:00am Eastern Time in the U.S. (which is only 9:00pm Pacific Time of the day before, and yes that is weird, but it seems like the most official way to go). Sometimes there may be a limited number of whatever the surprise is, so the earlier you check it out, the better.