Never. Every healthy fan leaf you remove is taking away that surface area of energy that plant could be using to bulk up your buds even more I would only remove dead or dying leaves with auto flowers any stress in the early flower can cause big problems going forward in my experience anyway even my photo periods i will not defoliate until the first 25 days of flower cause i think the plant is already going through quite a large change adding more stress on top of that i just dont think is worth it for the result though thats just my opinion your plant you do what you want lol