Day and night are not really equal on the equinox, which occurred here on the east coast of USA on Saturday 21:54. Daytime starts when sun's orb begins to come over horizon and ends when it disappears. Also, sunlight is refracted over horizon.
That means on fall equinox, day is still longer than night. A few days after fall equinox, and a few days before spring equinox, day/night is actually pretty equal. Today, daylight will be ~2 minutes longer than dark and tomorrow, ~1 less.