Experience
In partial answer to your question, I never play when I am tired to begin with. I never play to any set level of win or loss.
Based on vast published information, trip reports on various websites, and my own experience, I typically play 1.0 hour at SD and 2D, and 3.0 hours at 6D. I typically spread 1-6 on 1D, 1-8 on 2D, and 1-16 on 6D. I am a low roller ($5 & $10 minima).
Sometimes if scrutiny from the pit is at a low level for various reasons, I will stretch a 2D session to 1.5 hours, although this may not be a good idea, as level of scrutiny from the sky remains an unknown. I have never, to my knowledge, been stung by this yet.
I have been told by a forceful and aggressive expert that 3.0 hours on 6D is too long, although, once again, I have never, to my knowledge, been tagged by it, and the person offering the advice did not cite any actual personal experience to back up his opinion. I believe his advice was geared to high rollers.
I tend to spread my activities pretty far and wide across the country, so tend to hit LV pretty hard (boosting bet spread) when I go there, more than one would do if a resident there.
Despite not playing to any stop-win or stop-loss, the graphs of my results looks pretty much like textbook statistics diagrams.
Cheers,
:: ::