Be careful with this, as something like this can quickly get out of hand.
I agree with Denver, try to set a specific goal. eg. if you win a fair amount of money, and you feel that you're not winning anything else for like half an hour, an hour, stop playing. Or you'll lose your winnings.
Also perhaps you should try to put a time limit on your pokergame if you have addiction problems and it affects you emotionally. If your average playing time now is 12 hours, try to go down bit by bit. Depending on how much you are willing to take off at a time, this can go fast or slow. I think everyone has their own time limit, but try to remember it as the following: if poker starts playing with you, stop. Tomorrow's another day
I hope this helps for you, don't hesitate to ask for more advice if needed.