Outdoor growing

Generally a plant will begin to show signs of flowering well before the equinox, just the steady decrease in light is usually enough. Some pure sativas are a bit more picky though. Those tend to do better closer to the equator when grown outdoors. If you're too far north or south(I'm guessing south for you if you've been growing outside for 4 months already) the combination of light cycle and seasonal length make growing pure sativas pretty well impossible without a greenhouse or something.