24 hours. If you are at Pole, you get 24 hours of daylight. Your daylight at lower Antarctic latitudes (e.g., 89S, 77S) is a trig function of that latitude with a little variance. read more
Equinox happens to be a 24 hour day in both poles irrespective of the autumnal or vernal equinox. Right after Equinox constant day and night conditions begin in poles. Below is a picture to show the Sunlit hours on various latitudes during a year long period. read more