Teach me your ways man, give me all the brujeria tea

Me!

Leave it blank and let him decide

It is not too late. You would just need to submit your materials before then (before Jan 15 is usually the priority deadine) and let them know you lsat score will be coming later. I would only do so, if you are confident on your ability to take exam. For example, it is not your first time taking it and you are looking to raise a few points.