AA 4504 then UA 551 at O'Hare
South Bend → Chicago → Des Moines
Timetable, Chicago time
18:35AA 4504 from South Bend at the gate
16:05UA 551 to Des Moines leaves the gate
21 h 30 apart on the timetable, overnight
UA 551 leaves 21 h 30 after AA 4504 arrives on the timetable: more than half a day, so not a connection we count.