Pruning underneath canopy

So I am new to scrog but I am giving it a shot. I have a ex cheese and a Kalashnikova from greenhouse. Both plants are doing really well the cheese is filling better then the kalash but the kalash is bushier than all get out, just not all coming to the top of the screen like the cheese. The kalash is growing wider while the cheese is growing taller. The question I have is when is a good time to cut/trim the lower branches and shade leaves. I dont want to cut to soon and stress the plant but I dont want to cut to late and draw all the energy to rebuilding the leaves.

It should be a gradual thing through veg, with the final clear-out a week or so before 12/12. Use the prunings for cuttings. That way you get 2 or 3 goes at the cuttings.