personal opinion: Prinston is not so useful. The questions are so different from GMAT and a lot repeating questions. I got 690 in my first mock test of Prinston and then 730. And then I just didn't do them all. I think Kaplan gives you some practice of how to manage the test in the given time because it's very challenging if you want to complet its test. So if you can at least finish the Kaplan, I believe you won't need to worry about the time in your real test.