You can top anytime .... I like to wait until it's good and booming before I put heavy stress on them but they are resilient little buggers and always bounce back we topped about 3 weeks in the first time but u can do it as many times as you need to keep you canopy level...
New update on the outdoor grow
After hst lst and topping I have trained them right across the floor on top of the soil aiming to keep them low as possible
@InspireMe, keep a close eye on the coming weeks mate things are about to get exciting haha all the best on your grow aswell ill have my fingers cross for you