Soooo I kept thinking this was a loading issue on my end, and some quirk of Unity. But in case it is a bug, I have loads where the starting cycles for the fastest build/harvests take two seconds, and where they take one to nearly two minutes. And the buffs don't seem to make a substantial difference either way.
So in the slow cases, those games take 10-11 minutes at my quickest hack. Or there's the speedy ones that take 5-7 minutes, and that's with everything producing so fast that I lose all my mined stones from overflow and had to start from scratch* at the last moment. And right now my connection keeps cutting out and I have a ton of programs and tabs running concurrently. So it can't be on my end. That is... a significant discrepancy in gameplay. *If I'd started over mining on a 'slow' load, that would've taken nearly 12-13 minutes.
I say 'loads' bc this one has been sitting in tab for my whole session, and it's still fast. If I were to reload, I might get another fast one. Or more likely it would be molasses.