I top 7-10 day before putting them into flower. Topping early changes the structure of the plant cells and in my case made veg 10 days longer. Early topping was one of the first techniques used in the starting days of indoor growing and comes from outdoor growers not wanting to make many trips back to their patches, so they topped early for their convenience. It works but since then research has shown better ways. Its kind of like booze, its not good for adults but can cause real health issues if given to children.