I give my plants a major defol 3-4 days before I flip. Gives them a few days to recover. Day 21 ish I do it again.
Since you already flipped, I would just pluck big fan leaves until it is open enough that air is moving throughout the whole plant.
I agree with Gmix that at this stage 10% removal should be the max. If you need to do more, wait 3 or 4 days. I would clean out the bottoms
at about day 21 or when it stops stretching.
Having said that, remember that our favourite plant is a weed. It will adjust to whatever conditions you provide. Some plants like to be left
alone and others want that haircut.
Plants look great especially for a first time grower. It looks like you have 4 plants there. What strain ?
During veg I am plucking anything that impedes air flow.
Maybe next grow try light defol on 3 and go hard on 1. You will learn a ton about your plants and growing in general.
Good luck.