Surely, the student pair will have a set of course/session/endorsement/recurrency notes for reference ? If this is the case, as it should be, the pilots should be turning up for the session already well-briefed.
The pre-session instructor briefing then should be a recap and discussion session to detect any errors in understanding so that, when the group gets into the box, things should be able to move in a productive and interesting fashion.
The post-session brief should, again, be a recap with discussion, as appropriate, on things which might not have gone as well as expected. In that case, of course, a sensible session will have spent a bit of time on revision/practice at the time to get the folk up front on top of whatever may have presented a problem.
As for several hours pre-brief, after 30 minutes (unless the presenter is very skilled and interesting) I'm restless and, by 45 minutes, quite lost to the cause. Waste of time, in my view. Same views on classroom coursework - max 40-45 minutes and then a 5-10 minute break.
Sheppey, whom I have known and held in high esteem for many years, is a very experienced instructor and a mighty fine one. His views are tempered with many decades of instructional exposure ...
Or am I just an old dinosaur sort of instructor and over the hill ?