Always harvest based on the ripeness of your trichomes. That is the only answer under a normal cannabis indoor grow. Outdoors factors like weather can throw a wrench into the gears, but just because your plant is fox tailing doesn't mean panic and chop. Get the temperatures down in your space is they are high. Keep your humidity in the 40% range.
And check the genetic's of what you are growing because these days there's so many fucking bullshit fuck head "breeders" out there that are here to cash in and don't give a damn about the craft of producing solid stable genetic's that you really have to be careful. The breeders that were around 30 years ago, are breeders you can trust. They've been doing it with passion back when there wasn't a "autoflower cash cow" group of dumb fuck growers out there that love buying and buying and buying and re-buying and re-buying auto seeds.
Barney's Farm, Sensi Seeds, DNA Genetic's, Green House Seed Co. are breeder's you can trust. There are certainly other's out there, but you have to do your research and homework. Otherwise you get foxtailed out hermaphrodite plants.