It takes 10 hours of light to make THC. So the end of the light cycle or just before lights on when she is through sending sugars down the plant. But really the time is when she is ready, the smell will lessen in senescence as she gets ready to die and you have a window of several days before a few amber become 50% amber. Some strains will surprise you with a late burst of growth. Watch for the false seed pods to swell or cut a small piece and put it on a hard surface and scope it. If you want to flush, but run out of time, give ph'd water in excess for a couple of days and it will leach the nutes out some.