I think it may be useful to know that Robert does perform at a reasonably high level. Getting through 2 hours is not an issue.
This is a good place to talk about getting a life. While it is true that we usually CAN make pracice sessions compact and get most of what we need to do into single, max 2 sessions, you should think about the possibilities of taking longer breaks.
I often criticize "not thinking" or beating up the chops. IF we have the luxury of time (and we probably do more often than we realize), then I believe Roberts way has GREAT advantages - not only in keeping the chops fresh, but also the mind. Concepts can sink in BEFORE being repeated. Questions can be intelligently dealt with without interfering with the practice flow. We get used to practicing without pressure.
I recommend that some of you try something this extreme. You may learn something about yourself.