the things people used to say about flushing have been proven wrong. now, they make up new reasons. this is obstinate behaviour and a giant red flag with blinking neon lights sorrounding it and one of those whacky armed inflatable tubemen nearby drawing even more attention from traffic.
flush if it makes you feel good.
whether soilless / hydro / soil grow will impact when you should flush. Soil you flush longer, and soilless maybe a few days, and hydro maybe 48hours?
consider this... outdoor is okay right? and in good conditions it will grow just as good of weed as indoor, though chances are you don't have 100% sunny days over 3-4 months, but still.. now, do they flush the earth wees before harvest? lol, no of course not, because that would be fucking insanity trying to flush the earth of the stuff that provides NPKCaMgS + trace elements. insanity.
trichomes on calyxes, not leaves (30x magnification needed)
pistils - color change
density of buds
use all three to determing your harvest point. some of these can vary by genetics, so it's good to use more than 1 observation to decide. read up on it, sure, but do try early-to-late window harvests so you know you are finding what you prefer out of your weed. the example i liek to use is common cold medication, like nyquil. some people fall asleep and a small majority will get hyper from nyquil. I'm in a coma within 30mins of takng nyquil, lol, but not all experience the effects the same way. Same with weed. there is deviation person to person, though not often drastically different.