I think it is difficult to gauge how good/bad an interview is based on the length of time said interview took. It depends on a whole slew of factors.
1. The phenomenon of the "psycho" pile. The "psycho" pile is a pile of candidates that adcoms set aside for acceptance unless at their interviews they appear to be immature, rude, uncouth or otherwise inappropriate. These "psycho" pile interviews run differently and can be very, very short, as once it is established that the "psycho" candidate is acceptable, the "psycho" candidate is accepted. At Tufts the Dean of Admissions discussed this a little--he said that some interviews just have a weird feel about them, questions seems a little off-topic, etc., and that often this means that the interviewer already knows where the candidate falls...
2. Personality connection. Say you discover that your interviewer spent six months of his/her life living in what you consider to be the most wonderful place in the world. You will have plenty to discuss with said interviewer, which may end up making the interview very, very long. This is good because, well, you have connected with the interviewer. But although a personal connection such as this makes things easier, is not necessary. Furthermore, real personal connections can only develop when the interviewer has enough time to just sit around and chat.
3. The busy doctor. Most times, I would say, interviews that are short are so because the interviewer is busy. They may be seeing patients, they may be running late after dropping their kids off at school. Life tends to get in the way of tasks, you know?
So, what I would say is, don't stress about short interviews. Chances are that the interviewer's time got eaten up by something else. (I personally hate short interviews--I feel there is no substantial amount of time to, I guess, let the interviewer know who I am. This is why schools that schedule 1/2 hour interview sessions make me nuts. Conversations should flow as they flow, you know?) The fact that the interviewer can only give you 10 minutes is not your fault or any reflection of inadequacy on your behalf (unless you walk in insulting the guy or picking your nose or something--that's not good
).
And, remember, 10 minutes with an interview is better than none. That's 10 whole minutes to show the interviewer just how awesome you really are!
Good luck with interviews, everybody!
mma