They are healthy clones and are now babies heading towards teens. I heard the time to start topping in plastic cups is when the plant reaches 15" inches tall. Does that sound right? Thanks.
A seedling will have opposite leaf sets then at sexual maturity show alternate phyllotaxy. Hence clones typically have these uneven nodes too and I find topping to be less successful at this point: it will encourage new growth but the higher shoot on the node tends to dominate in my experience. This is why I only tend to top a clone once or twice max and LST after that.
I'd love to hear from people who do it differently with success.