With STS i usually spray once every 2 days for say 3-4 applications then spread them out after that until i see pollen sacs forming, to me spraying a bit heavier at the start is sometimes needed it seems especially if they are already into flower a decent ways as you need to knock back the ethylene production in the plant.
With autos ideally say 3 weeks after emerging from soil, though i kinda like to wait and see some plant structure first for selection purposes which is more week 4.5+ but then you have to knock back the plant harder and you run the risk of plants finishing before you have a chance to use any pollen produced if your running them all at the same time.
Depends on how many seeds you want, like if you just want a couple those early nodal calyx’s that form just at the onset to flowering you can get a good 20-40+ seeds off a small plant if you pollinate them then and you still have sinsemilla buds as well as the seeds are only at those base node junctions which are easy to pick out when trimming, now if looking for alot of seeds do so when the plant is bursting with calyxs and new pistils which is say week 4.5-5ish with autos most of the time.