I trim my lower buds right when I throw them into flowering mode. You should be able to see the small buds about to form after about a week into and just pinch them off. About 3 weeks into flower I also look to see what small buds are forming on the lower 1/3 of the plant. Pinch those off. Now after that I don't usually mess with them. It's too close to the end of flowering to stress them out a bunch. Those lower buds don't amount to crap and will take away potency to the other bigger, better buds. Try it a few times and you'll get the hang of it and see what will become of your plants.
