The spores have to fully colonize a jar before they start making mushrooms. If you start off a couple jars with a lot less substrate, then they'll be colonized quicker and produce mushrooms quicker, although they won't produce as much. If you mix the spores and the substrate together somehow, then the substrate will also be colonized quicker, although there will also be a higher contamination risk.
Just using plain brown rice, I've had 1/4 cup of substrate (x 5 jars) fully colonized in 17 days, and had enough mushrooms to trip on in 24 days. But if I had done twice as many jars, with half as much substrate, I probably could have gotten them even quicker.