Hey man, i've seen it countless times on GD, topping an auto too early. Folks say you can't top an auto but i've seen folks flux and auto and pull almost 200 dry from that. Basically there are two kinds of autos, fast ones (likes GSC) , and bigger ones (like XXL Amnesia), bigger ones respond to training better. Depends on the strain also, but basically you want to check if there has been enough growth at the bottom of week three, if so then go for it, if not then go for it at your own risk! topping is great to increase your yield, so go for it!