The Vernal Equinox occurs today at 11:57 AM CDT. The term equinox references equal as the length of the day and the night are both 12 hours in length. Yet, if you look at the sunrise and sunset times for today, you will notice that we actually have a bit more than 12 hours of daylight. The actual day that we recorded 12 hours of daylight was this past Monday.
Why Monday and not today? It comes to the difference on what part of the Sun is used for the measurement of when the sun rises and sets and what part is used to measure the time of the equinox. The Vernal Equinox is the time when the center of the Sun crosses the equator whereas the sunrises and sets are measured when the edge of the Sun is first visible or last appears. That subtle difference of location is the reason why the equinoxes are not necessarily equal when it comes to day and night.