Personaly you will see alot of different answers to this hot topic question as many growers will train there plants in varying ways ... I haven't done heavy defoliation before lights out I'm usually doing it a few hours after lights are on and then it's alright to start and then maby I'll come back tomorrow and finish up so as to not stress the girls to much ...I would assume you could do both ways yet once you do it and lights are on those leaves start peeking right up and reaching for the light... They want that light after to draw energy and recover.. As long as they are healthy and doing good light pruning will help with air flow, light penetration , and humidity or mold problems it a very valuable tool to have at your side ... I would let those girls go another week and then pick ones that really take away from bud producing sites..cheers