I think a couple of you have taken my point a little too literally. In there somewhere, I said that there's an optimal point in terms of duration/focus and the goal is to lengthen it. It will, of course, be -EV to grind when your eyes are unfocused and brain like mush!
The gym analogy works absolutely fine as I used one and two hours as an example and not the hugely-impractical three hours plus. Assuming that it's not physically damaging (which it certainly shouldnt be for your average pretty-fit guy,the fitness equivalent to OP who says he can grind 3 hours before stopping), then anyone looking for optimal time usage/reward would achieve more in a single 2 hour session than two separate one hour ones.
So there's really no need to nit up over the details here and instead try to take on board the larger point being made
No analogy is perfect as no two circumstances are identical, but they exist to make a concept easier to grasp and that's the goal here.
Also, a HUHyper player need not take onboard this advice as the loading/wind down is minimal. From 6max turbos plus, this is very relevant. A 9man player who plays lots of short sessions is damaging his hourly rate considerably.