Just to get technical & answer a few questions that may be out there, here is wikipedia's explanation of the Autumnal Equinox.:help:
An equinox occurs twice a year, when the tilt of the Earth's axis is inclined neither away from nor towards the Sun, the centre of the Sun being in the same plane as the Earth's equator. The term equinox can also be used in a broader sense, meaning the date when such a passage happens. The name "equinox" is derived from the Latin aequus (equal) and nox (night), because around the equinox, the night and day are approximately equally long. It may be better understood to mean that latitudes +L and -L north and south of the Equator experience nights of equal length.
At an equinox, the Sun is at one of two opposite points on the celestial sphere where the celestial equator (i.e. declination 0) and ecliptic intersect. These points of intersection are called equinoctial points: the vernal point and the autumnal point. By extension, the term equinox may denote an equinoctial point.
An equinox happens each year at two specific moments in time (rather than two whole days), when there is a location on the Earth's equator where the centre of the Sun can be observed to be vertically overhead, occurring around March 20/21 and September 22/23 each year.
There it is! Keep in mind the further away you get from the Equator, the quicker the day/night lengths change. I.E., locations nearer the Equator remains relatively close to 12/12 year round, while locations further away experience large & rapid changes in day/night length, as the days move toward or away from either Equinox.:sun2:
Now to answer the question, "When does flowering start?" In previous discussions about this, we have reached an agreement that indoors it begins with a flip of the switch to 12/12. Outdoors, it begins when you see pre-flowering & the days are shortening. Every strain will begin at a different amount of light, some with 14 hours or more, others much closer to a 12/12 split.:punch
