Having seen Mosconi shoot a number of times, when he was well past his prime, my opinion is that: had he been offered time on the same table as JS's run, and while in his prime, it would have gone something like this:
He would have walked in, taken his jacket and tie off, shot a couple of warm up racks and said, "Let's go." Then he would probably have run some number past JS's number, laid down his cue and said, "I'm hungry. Can we get a sandwich?" After eating he would have picked up his cue again, go well past 1,000 balls and then looked at Bobby and ask, "How long we going with this?" Then he would have run a few more and said, "Let me know when someone gets past this run and I'll come back beat that."
As to conditions? Probably the most pertinent one would be that Mosconi wouldn't need weeks of repeated attempts on perfect equipment and with ideal conditions. He was used to walking into a different pool room packed with people, 300 days a year, with a variety of environments, take two warm up racks, and run 100 virtually every place he played.
So, IMO, Mosconi would have run balls on the JS table for-ever.
Lou Figueroa