I'm usually good for 4-6 hours.
The hardest was three days back to back, on my left arm.
Last year, I moved from Chicago to the west coast, and the move happened as I was finishing a steampunk sleeve project with Larry Brogan; we needed three or four more sessions. He had a guest spot coming up in Grants Pass at Jeff Gogue's place (Off The Map Tattoo) so I booked three of the days. I figured it was a lot easier than flying to Chicago three times.
The first day was fine. We did 6 hours.
The second day was fairly rough, very tender. I felt everything. We did 5 hours, then went for pizza and beer.
The third day, totally brutal; my arm had serious swelling (looked like edema). It was painful from the first jab to the last. Larry really did his best and was concerned, but I insisted. From a pain point of view, it was brutal. In the end, it healed perfectly and there were no issues. Pain is temporary, awesome tattoos are forever.
I attached a pic of the upper part of the sleeve.
Won't do that again!!