Right. He need to stayed at airports. Because its will be missed the flight. I think he need change the flights instead of 4 hours layover in ATL. I have been long 3 hours layover in ATL from last year in 2007. I look it around where I watch the planes is in concourse E. I still have more qualification time during long layover in ATL. I will expect to fly more during mileage runs.
I think you should let's him to stayed at ATL inside the concourse instead of leaving from the security. It will be long lines at the main checkpoint. You don't want to wait for your turns to get through again. Because ATL are very extremely busiest hub with DL & FL, too. Hopefully if he need to understands where he must to be stayed in ATL airports.