AA 4504 then UA 4438 at O'Hare
South Bend → Chicago → St Louis
Timetable, Chicago time
18:35AA 4504 from South Bend at the gate
10:45UA 4438 to St Louis leaves the gate
16 h 10 apart on the timetable, overnight
UA 4438 leaves 16 h 10 after AA 4504 arrives on the timetable: more than half a day, so not a connection we count.