Fast or early labelled seeds are photoperiod indica crosses with a bit of ruderalis mixed in, so they still need the light flip but finish a week or two sooner. In practice that means seven weeks of flower instead of nine for some lines, which helps outdoors when autumn rain arrives early. How these differ from true autoflowers, and which breeders deliver the shorter time, is compared on https://kushindicaseeds.com with grow reports attached. Yield tends to drop a little, so it is a trade rather than a free upgrade.