All of the packages have available dates written at the top of the page. Often they say if the properties aren't available during the holiday season. That said, you should probably call the property first before bidding if you really can only travel during the post-Christmas week. Was there a specific package in general you are looking at?
You could do a search of the package by month of travel, which should return only those packages which are available in December. If you don't see anything you like now, you could keep checking back as there are new packages being listed all the time.