Its not the transit time that gets you, it’s the unplanned 6 hours on a 95* runway in DFW or Atlanta waiting for a delayed flight that gets you.
REGARDLESS, if the meat was put in the box unfrozen, and then froze solid, it’ll take several days to thaw. Think about how long it takes to thaw a 20lb thanksgiving turkey at room temperature, its days. I know guys that routinely fly home with frozen meat in just a box. An unplanned overnight on a runway would be an issue, but they never had a problem. That said, a contractor bag around the box, a sheet of home depot hard foam to insulate it, then into a second cardboard box, is as good as most coolers, and lighter weight to help avoid excess fees. No dry ice needed unless maybe its just for the overnight before an early flight.