Question:

[PlutonianEmpire]

I was looking at my weather calender for this year, checking out the sunrise/sunset times, and noticed that for my region (Minneapolis, Minnesota), sunrise is at 6:22 am, sunset at 6:21 pm (Central Standard Time), on the seventeenth of march, when the sun doesn't "cross the equator" until march 20. why is there a 3 day difference between the exact 12 hours of daylight, and the vernal equinox?

[Hamiltonian]

Refraction.
Atmospheric refraction delays sunset and advances sunrise, so daylight lasts longer than twelve hours on the equinox.