I would just assemble it fully and say its an early Christmas present. You will be stressed to the max trying to put it together Christmas Eve especially since you need to cook that night too. Plus these things are never straight forward there is always some kind of problem that pops up. Plus it will be dark and you'll be tired. And sometimes there is a certain way these things need to be constructed so you might not be able to partially construct it. You could get the instructions out and have a look.