Have they slowed or stop stretching? Four to six weeks is usually the time frame. Nirvana's Flower Tabs work for at least six weeks. They are also organic, so they say. You could go a full tab, but I'd side on caution and stick with a half. You can push the Flower Tabs in at any time now. Try and brake the whole tab in half or thirds and push them well into the soil I'd do half a tab each including the little one. Then wet/dry cycle. I'd add cal-mag and molasses each week during flower. Cannabis Autoflower's can be cal-mag whores so BE PREPARED. After four weeks see how they are. Add a quarter of a tab if needed then. You got two weeks of flush coming anyway. My grows at least ten weeks. I like my buds like a ripe banana. Half a Flower Tab should get you through to harvest. Additional bloom boost would be okay late in flower too. Just don't over do it. Chester is the Nirvana's Soil/Flower AFN Expert. His grows are out of this world. I want to be like him when I grow up.
NOTE:
I have a Toof Decay Micro Grow. I treated both my girls the same with water/feed. The little one rebelled and curled up like a kayak. Have to back off on her and let her ride it out. My point is I didn't pay attention to her and pushed her too hard too early. Your girls will let you know what to do.
Good Luck.