How long does a good interview last?

I’ve already done my interviews quite a while ago but I’ve been reading posts of people who got into the schools I am applying to, and many say their interviews lasted over an hour. My interviews ranged from about 20 to 40 minutes. Will this lower my chances of getting in?

20 to 40 minutes sounds adequate.

I know it’s easier said than done, but try not to read into things like the length of your interviews. The sample size here is VERY small relative to the total number of applications and acceptances each year. Can you imagine if all the interviews of kids that were likely to be accepted took an hour each? Congrats on having them behind you and try to focus on what you need to do to complete your applications, if anything. And enjoy your friends and family as we head into the holiday season!!