Could I take the GMAT in Sept 9 and Sept 25?

Dear Matthias15,
I'm happy to respond. To be honest, I don't know the exact answer to you question, but I am going to chide you. WHY ON EARTH would you want to take the GMAT twice in a month? WHY ON EARTH would that be a desirable thing to do?

The goal of the GMAT is to impress b-school adcom. If you take it once and achieve mastery, that's very impressive. If you take it once, give a mediocre performance, and then perform with mastery on the retake, that's still pretty impressive. Two mediocre performance in a row are not a very good track record.

Sixteen days is really not enough time to make substantial improvements of any kind, so it is more than a little bit likely that you will get about the same score both times. If it's a excellent score, you only need it once. If it's a mediocre score, it's not going to make a very good impression to have two back-to-back mediocre performances.

My friend, do not underestimate the GMAT. Everyone who takes the GMAT already has a college education, and many of them have bought a book or a service that provides them with high quality prep information, and yet of this extremely talented, extremely well prepared pool, only 10% every achieve more than 700. Excellence on the GMAT is no small thing, and not to be taken for granted.

Does all this make sense?
Mike