I don't flush, I feed till the end. Flushing is Bro Science.
Studies have been done on flushing and results say that plants with zero days of flushing have the smoothest smoke and best flavor.
When you look at Trichomes, don't look at the leaf trichomes because they mature faster.
Look at the actual buds and calyx trichomes.
As far as trichomes, I harvest based on if they're Indica, Sativa, or a balanced Hybrid.
When the bulbous heads of the trichomes are fully developed but still translucent, plants will produce a "high" and stimulanting effect, less sedative. It is the perfect moment to harvest strong Indica strains.
When these bulbous heads turn milky is probably the best moment to harvest most available hybrids.
When 70% of these trichome heads are milky and 30% amber, it is the perfect time to harvest mostly Sativa hybrids and long flowering strains (like Haze).