Today, I had an interview at Phillips Academy in Andover. It was nice and friendly but I felt that most of the people there were on a different level. When I was doing my interview that seemed to pass by, it felt like 20 min. But when I was done I found out my interview lasted an hour when the rest of the kids there who were getting their interviews only lasted 20 min. So the question I have was, is it bad that my interview was longer than the other?
Do not attempt to read anything into the length of an interview. Assume the interviewer kept you as long as necessary to make the interview worthwhile. You are the one in the best position to know if the conversation was pleasant and enjoyable, forced and uncomfortable, or somewhere in between. The length of the interview is unimportant.
It is not bad (or good). The interview is part of the process to get to know you as a person - to learn things that aren’t on your application.
It doesn’t matter how long your interview was. Interviews are mainly to let the schools know who you are not on paper. your interview may longer depending on how much you connect with the interviewer. As long as you feel like you showed the interviewer who you are as a person the length of an interview shouldn’t matter. GOOD LUCK 
!!
Interviews are generally about “fit”. They are not trying to assess your qualifications (they’ll have the rest of the application for that). They want to figure out if you are the kind of kid who will thrive at their school, get along well with others, take advantage of what they think makes their school most special, etc… and they also want to get a sense of whether you will attend their school if admitted. They don’t need to keep interviewing you once they’ve figured that out. A longer interview means they were enjoying the conversation and didn’t have an interview scheduled immediately after yours. Our daughter had some really long interviews (one took an hour, if I recall correctly!) and one incredibly short one. She is currently attending the school where she had her very shortest interview (15 mins!)