Hi!
I do the first defoliation when I switch to flowering (the same day), but only the main stems. She'll recover from the stress in the same time she realized the photoperiod change.
Then, I do it again 2~3 weeks later, when I add guano powder to the soil (more phosphorus for more flowers).
But as Fempkid told you, your plants must be in a good shape to support that kind of stress.