8:30 Atlanta time is 7:30 CST. Since the Ramseys were flying in a small private plane, I think it would take longer then an hour to get to Minneapolis. I've flown there from Denver, and it was an hour in a large jet.
I recall reading somewhere that it actually would take several hours to fly from Boulder to Charlevoix, Michigan on a plane that small. It was something about "spending most of the day on the plane". Even on a commercial jet, it takes longer than a hour to fly from Colorado to Michigan. That's elapsed time, not accounting for the time zone change.