I would not recommend doing a full NBME the day before the exam. I did however do like 50-100 practice questions from NBMEs the day before (I had also been doing this every day during my dedicated). Some of the NBME questions pop up word for word on Step 1, so I didn't feel like it was a bad strategy.
My opinion: you should either take the full day off, or 1/2 day off. The day before I was reviewing pure memorization things (embryo stuff like aortic arch derivatives, random pharm, things which I was forgetting). Actually 2-3 questions on my Step 1 came from things I reviewed the day before (maybe would have gotten them right anyways, not sure). It's certainly not a bad strategy if you're reviewing things you've forgotten (like stuff that is pure rote memorization).
A good night's sleep, exercise, and a positive attitude will do more for you than any studying though. I took off at like 6 pm the day before and was able to get really good sleep. Don't try to pull an all nighter or make yourself nervous.