Extended darkness before harvest will just slow your plants metabolism unnaturally which can cause THC to break down to CBD and CBN due to the almost zero metabolism and I would say, your plant would be traumatised, not an ideal situation if you are after prime flowers. I, after years of experimentation, have developed a preference for harvesting about an hour or two after lights on/sun up and after a normal one nights "sleep". It seems harvesting in the afternoon produces flowers with less terpenes, possibly because by then the plant is in full energy producing mode (photosynthesis) and the terpenes have either slightly evaporated or somehow "locked away" against the heat. I have discovered that the tastiest trichomes and most pronounced terpenes seem to be, as I said earlier, at their highest levels after a normal nights rest and about an hour or two after the metabolism is boosted by the arrival of dawn or lights on, if growing indoors. I have over the 35+ plus years that I have been growing, experimented with harvesting and also taking notes about which times I have harvested, anywhere from dawn, early morning, late morning, midday, early afternoon, late afternoon, sun set and even in the middle of the night, which incidentally produced the blandest flowers, followed by afternoon and sunset harvests and with the early morning harvests being declared the winner by me. Hope this helps,...
Organoman.