Let it go until older bigger leaves turn yellow. If it's still going, let it do it's thing. I only done a few autos and hated them. Too problematic, not enough yield. I can get them almost same size as photos, but the output is way less and seem more susceptible to disease, mold, and budrot. Different strokes, different folks, I guess. As for when to harvest, I always watch for the buds to finish swelling at all the pistils. With exception of the bottom of the plant,as I usually lollipop.