@R1onsnoopdawg, It depends on how much nutrients you have been feeding them, I usually do a 10-14 day flush, some plants may only need 7 days. The way that you can tell is once most or at least quite a few of the leaves have started to pail and turn yellow, the idea is to use flush the soil and use up all of the nutrients stored in the leaves to get a nice clean smoke, so once you see those leaves yellowing your ready. I usually like to give them a couple extra days of flush and then give them 48-72 hours of darkness to help shock them to bulk up the trichs