I've got the basic idea about cutting off the lower third of the plant growth to concentrate everything to the main stem but I'm curious about what time to start pruning the plant?

I'm using an aero system and they've been vegging in there for a week and a half now, about 8" tall I plan to flower once the first one reaches 12". I was curious if pruning while only 2 weeks in was ok or would this hinder the growth since they're still so young?

If any of you have some good pictures, or general guidelines about lollipopping I'd love to hear/see them.

Thanks!