Topping autoflowers

You shouldn't top an autoflower, they do not have sufficient time to recover within their fixed growth cycle. Autoflowers are suitable only for Low Stress Training (no topping, fimming, supercropping, etc).

Lst bending plants horizontal is a great way for autos and photos with or without topping .I've topped autos for years with great results at 8 node when growing horizontal .way better than straight up waste of light plants

And btw, even with photoperiods, you never top them when they're in flower... just isn't done.

Question: when can I top an autoflower? Answer: Never. Autoflowers inherently do not like major stress. Some people have been successful at topping autos but I consider them to be extremely lucky. Autos spend so very little time in veg (a lot will go into pre-flower in week 3), they don't have the time to recover from major stress - and if they can't recover, then their internal schedule is disrupted and they may never give you a harvest. For autos, stick only to LST if you want to be sure of having a smoke after all your hard work. Good luck!