<p>Use it now. You won’t run out of practice tests unless you are more than 10 weeks or so away from the test deadline. There’s 10 official SATs in the new Blue Book, there’s 3 online that you can print out (search around on these forums), and if you, for any reason, need to take over 13, you can always buy extra ones from princeton, barrons, or kaplan, although I wouldn’t recommend it because I’ve found so many typos in the writing section and critical reading section that it makes me doubt the validity of their answer choices. It’s best to do the official ones so you get used to the Collegeboard’s interpretation of things.</p>