i don't know for sure - i get it within about 24 hours of dropping the veil - i check the bin several times a day to ensure fresh air exchange. i do see spurts of growth around that time. i also see a richer/darker blue color at/after veil drop when i slice the shrooms. i am guessing that means more psilocybin but i haven't researched that.I thought you had to harvest before the veil opens for maximum potency.