I have a full back piece done in Thailand. I had to do fast, cause i left to do the tattoo in my last days of traveling! So... i did in 3 days straight, first day i stayed 9 hours ( fever and very bad afterwards), i don't even know how i came back next day, but i did for another almost 9 hours and in the third day around 5 hours!
Never more i could do this, and even now me and my wife don't know how could i do! lol