DL 503 then DL 543 at Atlanta
Detroit → Atlanta → St Louis
Timetable, Atlanta time
11:27DL 503 from Detroit at the gate
15:45DL 543 to St Louis leaves the gate
4 h 18 apart on the timetable
The last days
DL 503 and DL 543 weren’t both flown 15 min to 12 h apart in the last 21 days.
Statistics from past flights, not live flight information. Always check times and your connection with your airline, and don’t base travel or booking decisions on these numbers.