Well, I’m sure I would have the patience to turn the first gear long enough to move a gear 10-12 down the line, but moving a gear directly? Maybe 4-5, I’m not sure of the strength involved….
I’ve built a few Lego gear stacks in my time. I’m going to say 7, maaaaybe 8, but beyond that you’re at 1:256 even assuming no resistance, which is A LOT!
I would absolutely work at this until I got the bottom gear all the way around — it’s about the only fidget toy I could consider carrying/fidgeting with (at least until it was all the way around at least once).