Omg, I just wrote a pretty long post, added an extra comma, hit backspace and my browser went back a page, killing my post. Going to try to recover it.
I think your 9.09 BB/100 actually is sustainable at the stakes you're currently playing. Just the fact that you're winning at that rate already indicates you have a good idea of how to play, and that's pretty much all it takes for the first few levels, so well done there.
2-3 hours is a road block for me as well. In live play, I have played for 36 hours once, and at the end of that I felt similar to how I do after 4-6 online. I think it's mainly that in live play there's much more going on around you which keeps you aware, and alert, while online you simply stare at a screen where most objects are static. Anyway, what I've found is that after two or three hours, or whatever time I'm starting to feel fatigue, I take a short break. 30 minutes has always been enough, and often 10 or 15 is fine. My brain just needs a little time to decompress, and not have a few hundred hands an hour being thrown at it. So you might want to try playing 2 hours, taking a 10 minute break, then going for 2 more hours. You won't even have to leave your tables, you can just sit out and you should still have most if not all of your seats when you return.
Thinking things like "I'll get out with my profit yeah!!, 25% of my buy in ain't bad etc," can actually be a reason to leave a table. It is not theoretically, as (especially in limit) a table you are winning at is profitable. This indicates you have a higher skill level than some of your opponents whom you are exploiting. Therefore, the longer you sit at the table, the more money you will make. Try to instead think along the lines of, "I've increased my buy-in by 25% already? This table is going to boost my bankroll by that amount!"
Trying to protect what you've won is going to lead to sub-optimal play, which may not lose you money directly, but can still cost you exactly the same in leaving money on the table you would have won had you simply been playing your game instead of playing to keep what you've already won.
A great quote on this subject is from Mike Caro. He said something to the effect of, "Every hand you are dealt, no matter how much you've won, no matter how much you've lost, you are even"
And this is so true. When those cards are dealt, you have exactly as much money as you have. It doesn't matter what happened last week, last orbit, or last hand. You are even, and need to simply make the best decision you can on this one hand.
Further, you can analyze the table. A table is either +EV to be sitting at, or it's not. If the table is no longer profitable, then you should leave. If it is, then you should continue to play unless you feel you could be doing something else that's +Life EV. Say you're at a table, and there's a great fish, you clean him out, he reloads. After a few more orbits he leaves. You look at the table as it is and say, "I've still got an edge here." But how big is it? How much has your winrate changed now? Perhaps it would be better to take a break and go spend time with your kids or go fishing, or whatever it is you like to do. This isn't as big a deal yet since you're playing smaller stakes, but if you're playing for significant money, you can get in the mindset of, "I have to be here, I'm working and I need X hours a week." So a little ahead of myself here, but I got carried away.
Keep going with questions, they're good!