From my experience with a 510 atty, I generally go with 2 drops maybe 3. I know its time to add more when flavor starts to drop off or i get that slight burn (yuck). I try not to get to that point. Either way from my experience the with dripping the atty is going to flood to an extent over the course of a day so I generally blow them out at least once per day. After a blow out, i drop 3 drips puff a couple times then 2 drops from that point on.
Are you using carto's?