Umm it seems pretty silly to me. Sit and play for as long as you feel comfortable playing. Setting stop-losses is a sensible idea for many people because of the tilt problems that can result from a bad session, but setting what effectively are stop-gains seems ridiculous. What do you do if...
- You're sat at a table with 5 fish who are throwing money at you, but you just hit your 'stop-gain'?
- You have a bad session and 12 hours after sitting down you're still breaking even?
- You sit down and play decently for a while but after an hour or two begin to feel tired/hungry/restless?
Poker is one long session, not 3489673893 different short ones. Remember this! It seems like you're suffering from a not-too-uncommon problem of treating your winnings as if they're not real money
and hence throwing them around and hence invariably losing them. Remember that it's actualy money you're playing with - whether you started with it or have won it. Doubling that $100 buyin doesn't just mean you have twice the amount of pretend virtual chips and a number by your screenname that's twice what it was 5 minutes ago, it means a meal for two at a decent restaurant, or whatever.
Some people tend to get overly tight when they think of their chips as real money and not just a number and some pictures on the internet, but it's something that might work for you if you find yourself playing too loosely and haphazardly.