I had a 1pm interview, and I was the last one to go in for my interview with Dr. Norton. I was there until 5pm. Dr. Norton's assistant did mentioned that it was taking abnormally long that day, and normally it was only a couple hours from start to finish.
I had to wait so long because the five people ahead of me all took forever (about 45min each) and asked a million questions to try and get brownie points or something. In my opinion, the key is to get in, ask pertinent, relevant questions, and know how and when to wrap it up. His time is more important than mine, and really I can find all the answers to questions online or from students.