I once timed myself transiting ATL from the far end of the A concourse to the far end of F (so about the maximum possible distance between Delta gates at ATL). It took 15 minutes from door to door. I only had a messenger bag to carry and walked quickly, but did not have to run. I was also lucky as the plane-train pulled into the station as soon as I reached the bottom of the escalator. It was a 45 minute connection, and still had time to use the restroom in the terminal before boarding started. With that said, I would rather have a bit more time and lot less stress.