First of all, get a microscope and keep a daily look out on your trichomes.
https://www.royalqueenseeds.com/blog-knowing-the-time-is-right-to-harvest-your-cannabis-plant-n84
"Eventually, the resin will become mostly cloudy. At this stage, they hold the greatest levels of THC and will produce the most intense psychoactive effects. This is the point when most growers will want to harvest their crop.
If left longer, the resin will turn from a cloudy colour into an amber one. Gathering at this stage will produce a more narcotic and physical high."
and secondly regarding flushing, see this. Very informational.
www.youtube.com/watch
Good luck and happy growing