My average jetway to jetway time in ATL is 5 minutes if not changing concourses and 15 if changing concourses (using the train). If you're a fast mover (not running, but efficient) it can easily be done. However, I hate 40 minute connects because you're counting on the flight being on time, gate being ready, not waiting for the boarding door to open, etc. One wrong turn and miss your train stop could be disastrous also.

SR