AA 4504 then UA 638 at O'Hare
South Bend → Chicago → San Francisco
Timetable, Chicago time
18:35AA 4504 from South Bend at the gate
12:42UA 638 to San Francisco leaves the gate
18 h 07 apart on the timetable, overnight
UA 638 leaves 18 h 07 after AA 4504 arrives on the timetable: more than half a day, so not a connection we count.