Can I defoliate I am in the second week of flowering

Sure now is the Best time but you can do it perpetually aswell

I wait till around day 20 to 22 of flower to defol When you dodo b4 that time you allow more light to penetrate thru the plants. This can be a good thing and a bad just depending on how you plan to grow your plants. When you defol early then the power bud sites start to get more light earlier this causes the lower bud sites to start branching out more and strech for the sky. When you leave all the fan leaves in till after the end of the strech then the lower bud sites will have gotten less light and they would have stretched out less so most of the lower bud sites will stay all stacked to the branch’s compared to an early defol and lower sites branch out enough the start to make sub branch’s instead of stacked bud sites down the whole branch

Yes, second week of flower is the perfect time for a light defoliation. You can safely remove large fan leaves that block bud sites or heavily shade the lower parts. Just don't overdo it – focus on opening up airflow and light penetration through the canopy. Plants are still stretching now, so a clean-up will help them focus energy where it matters.