^^^ it depends on the strain, I was using fox farm for my autos and like you said you should start out with 1/4 of what it says on the bottle, and all you really need is some flowering nutes but then it all depends on the plant. my last grow with autos them bitches couldn't get enough of nutes, and I had one auto that didn't like nutes at all, so like I said it all depends on the strain. You can go over 1/2 dosage But you should never go over a full dosage.
You should start feeding your autos around 3-4 week mark, and go from there...they will let you know if they need anything, just keep an eye on them and they will tell you that their are hungry.