I have often wondered about that myself. Around the age of twenty I used to have many such marathon sessions. There was no need or pressure to do it, I was not studying music or playing it in a professional capacity, I was just determined to play difficult pieces and acquire certain difficult techniques. I was successful in that, but it is impossible to prove that long sessions had anything to do with it. That was fifty-five years ago and I am inclined now to think that I could have gone about things a good deal more sensibly and attained the same results if not better ones.