Equinox

I’m puzzled. 

In school I remember learning that March 21 was the spring equinox - the day when we have 12 hours of daylight, equal daylight and dark. I thought that, on that day, it would be the same in both Northern and Southern Hemispheres.

But tracking hours of daylight in our part of Canada, I’ve discovered that we actually had our spring equinox on March 16 this year - yesterday, according to my weather app... 

Or are hours of daylight calculated from dawn to dusk? In that case, wouldn’t our daylight hours be even longer?! Equinox, where we live, would have been a few days ago...?!