AA 5503 then DL 543 at Atlanta
Washington National → Atlanta → St Louis
Timetable, Atlanta time
16:16AA 5503 from Washington National at the gate
15:45DL 543 to St Louis leaves the gate
23 h 29 apart on the timetable, overnight
DL 543 leaves 23 h 29 after AA 5503 arrives on the timetable: more than half a day, so not a connection we count.