Had to prep a 5 minute lecture than a 50 minute lecture. The 50 minute lecture was interrupted a lot by comments from professors that did not reflect the types of comments students would get. It was hard to manage the time effectively. I have heard that this is common, but it makes sense for an elite school. I would prepare not just for comments you think students would ask (they may or may not show up) but also for those that you think profs would have.