MHM,
Congratulations on your interviews. That must be encouraging.
If they make you an offer, I'm sure they will give you more than a couple of weeks to respond (in fact, it will probably take at least that long to get an official offer to you). However, if you are a candidate they really want, they are probably going to try to pressure you to make a quick decision. They are going to try to gauge your interest in their program via the interview and will only make an offer if it seems likely that you will accept it.
Penn Stat and UT Austin are both fantastic schools, but they don't have the same reputational strength as Harvard, Stanford, Chicago, Wharton, etc. As such, they need to be much more aggressive when recruiting students. They need to try to get students to commit their programs before the elite schools start interviewing.
I would advise you to act very interested in their programs, secure an offer, and then wait for some of the other schools to make decisions.
Good luck!