How many times could/should I defoliate these Cobr...

I do what I consider 'real' defoliations twice, once at the beginning of flower, and again about 1/2 way into flower. But I will also do 'light' defoliations as needed throughout the grow - meaning if I see a leaf yellowing and dying off, I pull it.

Stick, is right. remove the largest leaves

Hi there! I'd recommend to defoliate 4-5 leaves max per session and let her rest for 2-3 days. Then see how she recovers, if it seems slow --> calm down on defoliation, if she's reacting well --> you can do it again. The important thing is to remove only the leaves that are creating shades onto your bud sites, and don't touch the non-blocking leaves since their role is crucial in energy absorption. Removing too many leaves can result in a stunted plant, slow growth/flowering, and buds full of tiny leaves. Hope this helps, keep us up-to-date and happy growing!

As long as you give them 1 week to recover before flowering, you can do it again. Next time would be after the stretch, at 21 days of flowering phase. Never defoliate just before the stretch ir during it, it can screw the bud site formation that happens during the first three weeks of flower