Hi car,
I think that's more than enough time. I studied for mine in 2 weeks. Nevertheless, I took the MCAT a few months before that, and had studied for 2 months for the MCAT. Have you taken the MCAT? If you have, then you are more than ready to tackle the NMAT. In my opinion, the MCAT is very difficult while the NMAT is so easy. It's all basic sciences. I was a Biology grad, who had some trouble with the MCAT but aced (90th percentile)the NMAT. So, if you have taken an intro bio, chem, and physics in college, don't worry. Also, I used this MSA reviewer book, which my friend bought from the phils.