They look like it might stunt them, you want them to have a good root structure before topping so they can handle the stress and at that size it doesnt look like they would have one so i would wait a little longer if i was going to top them. Id look on it at a plant by plant basis though if it was the right candidate for topping and with that being an auto and of smaller size i would probably look more into the LST technique. Happy growing mate 👌