I think it’s partly intuitive. This is going with about 250g in the hopper at a time.
I find a shot anywhere between 23-38ish seconds and 1>2 and 1>3 can be drinkable (obvs 1>3 in 23 might be sour etc.) The origin of the beans sometimes has a clue for grind size, e.g. if I am starting a bag of brazilian beans I’ll open the grinder up considerably, Colombians often need a tighter grind etc.
But generally for most beans I start where the grinder was set for the last batch, then make small adjustments or change the dose between the first few shots of the bag if needed, to fine tune and shorten or lengthen the shot.
It’s rare for me to pour a shot out doing it this way. But some beans can pull a surprise and need a big adjustment. Usually the grind setting and/or dose is about right within three or four shots. Sometimes a small adjustment is needed on the fly at seemingly random points in time.