Well, is there an alternate, earlier middle flight (MSP-ATL) that would give you a shorter MSP layover and a longer ATL one? If I were you I'd pay any change fee to make that work. I would not have bought your original itinerary in the first place -- I think it's always poor practice to try a short connect to a once-daily longhaul. Even if you make it the stress isn't worth the few bucks you may have saved -- look, the flight is more than five months away and you're already paying a price in worry. Low fare isn't everything.