AC 8547 then AA 3484 at O'Hare
Toronto (YTZ) → Chicago → St Louis
Timetable, Chicago time
13:20AC 8547 from Toronto (YTZ) at the gate
09:30AA 3484 to St Louis leaves the gate
20 h 10 apart on the timetable, overnight
AA 3484 leaves 20 h 10 after AC 8547 arrives on the timetable: more than half a day, so not a connection we count.