In any activity-hobby that requires constant time, there will come a time when you get tired of it) This is normal, I think) In poker, it is especially important to leave when you just feel tired), because if you do not do this, you can lose a lot more than your favorite thing) - money!)
A lot of players say, leave when the game has turned away from you, of course the cards may be against you, but I think it follows from the fact that you are tired and make mistakes at the table that you do not notice because of fatigue
I don't understand people who play 8-12 hours a day (every day), I don't know how to do it Lol... I think 3-5 hours if the game is going well and 1-2 tournaments at the same time is a good tournament day for poker, and any average player will be able to play such a session without any problems