I recently crossed over into the 2 hour mark. Though it felt like days. I was exhausted. Me and one of my ticklers have this game where if I don't get off the table when she's finished, she'll come back and tickle me more. So last time I was ticked for a continuous 2 hours, and a combined 2 hours and 30 minutes.
That's my current record, though it won't be hard for me to push past that. Even in exhausted bliss, I never told her to stop. I never do. My ticklers decide that, and so I'm thinking three hours wouldn't be to difficult for me. Of course, it's easy to say that now!