Would someone please explain to me how the times of school zone speed limits are determined? I don’t understand them.

I’ll be driving home from work, and see that a school zone is already in effect. I look over at the school, and the kids are still playing in recess. If school hasn’t let out yet, why start the school zone speed limit? Do the people who came up with the start and start times honestly think it takes drivers 30+ minutes to slow down before the kids are released? If a school starts at 8:30 a.m., for example, why have the school zone time last until 9:00am?

Don’t get me wrong, I do observe the school zone speed limits when they are active. That’s probably one of the few areas where I don’t take a chance at speeding.

On a lighter note, one of my Canadian friends that I met at NASA sent this funny commercial to me. He said that it wasn’t really Canadian, but it was a beer commercial.
You can watch it here.