This is a discussion on Limitations and goals within the online poker forums, in the Learning Poker section; When you go play poker should you have a goal sit amount or is there a set amount of time you have set to grind
The only amount I ever put on myself was hitting 30 hrs a week minimum, and aiming for 40.
Individual sessions, you can be having a bad day. If you're off your game it can be way more +EV (and + Life EV) to go golf that day, or do something else you enjoy rather than grinding hours while you're not on your A game cuz of a mandatory daily hour requirement.
I also don't really believe in poker stop losses or win limits. I feel I did well to objectively determine whether I was losing due to poor play or not, or to realize when I didn't have the right amount of focus to continue even if a game should still have been +EV.
That's the key, analyze the table, determine if it's profitable to continue playing. If no, are you still playing well and is there another table that would be profitable? If no, day's done.