Hiya DTaro!
Everyone has different opinions on defoliation however this is my go to route. I typically defoliate the 1/3 lower of the plant and remove anything that won't get much light. Once I flip to 12/12 I let them sit and then remove the big fan leaves and anything covering budsites, at the end of week 2 flower. I then let the plat grow out until the last couple weeks where I pick a couple leaves off here and there until harvest.
Cheers and good luck !