There’s lots of rumors of how the length of your interview pretty much sums up your chance of acceptance… Is that somewhat true? I had interviews with Exeter, Andover, and Lawrenceville. They went smoothly but were only a half an hour. I know some people who had interviews that were about an hour long. Does this prove anything??? thx
There is no truth to the idea that you can tell anything definitive from the length of (or even your subjective feeling about) an interview. Some interviewers make every candidate feel like they are long lost family who must spend more time with them; others will make even the ones they adore leave the interview thinking that they did something wrong. The biggest factor to the feel of an interview is the personality and style of the interviewer. You can drive yourself crazy trying to read between the lines to figure out what their attitude means, if you really want to, but you should not try to use that as a reliable predictor of your chance of acceptance anywhere.
Remember, quality over quantity. You could have a short interview and still put yourself out there! Or, you could have a longer interview and babble on and on and on…
Don’t compare how your interview was to others! Different interviewers, different applicant, different personalities, different circumstances. All that matters is how YOU felt about the interview, and if you think that it went extremely well and that you were able to show your interviewer who you really are as a person, then that’s great! 
What about interviews making most of students feel good and want to apply? Is it not how it works?
I’ve posted this before. DS interviewed at five schools last year and not a single interview was on campus or over 25 minutes long. He was accepted at all five (no FA)