I agree with you Rodney, and Clark Wilson has said as much to me. In early cinema, those players may well have put in 12 hour days, and I assume they had some breaks between audiences or films. I assume many were improvising and certainly more than one aspiring composer got into the act.
I doubt the Guinness people would allow any breaks, as the current world record of playing the piano (pieces, not improvisation) is 103 hours. Compared to that, my claim is negligible from a stamina standpoint.
I suppose I am also trying to document an extended improvisation session as well as an "accompaniment" record but again, with the performance record at 103 hours, they could easily reject my claim. If they do, I'll be taking my bathroom breaks between films, for sure (about 10-12 minutes each). That's easily doable and harder on the back than it is on the bladder, hands, and arms (for me at any rate).
In any event, it'll be an interesting day and it'll be a trip playing in the middle of a very cool exhibit at LACMA. Pretty surreal, really, and somewhat reminiscent of my days playing fashion shows in shopping malls for mimes in white face. I was also in white face, playing for them to act out little story lines to sell clothes from the shops at the mall. Not exactly the same thing, but not that far off, either. Funny!
There's going to be a fair amount of press coming out in a few major outlets just before it happens. That can't be too bad for business.

Be well, my friend. Have a great New Year. See you over at
Motunation.