From what I have been reading the asymptomatics are not a significant source for causal spread for the first couple of days, then each day their spread potential increases...
I have not seen a study that quantifies how that works, exactly (doubling, tripling each day, whatever...).
Info varies.
Seems a few days before they show symptoms they have seveloped a heavy viral load and are at least moderately infectious.
At the time the patient just feels ‘a little off’.
In a family situation even lightly infectious people spread because of the intimacy.