AA 1253 then UA 3376 at O'Hare
San Francisco → Chicago → St Louis
Timetable, Chicago time
17:05AA 1253 from San Francisco at the gate
11:00UA 3376 to St Louis leaves the gate
17 h 55 apart on the timetable, overnight
UA 3376 leaves 17 h 55 after AA 1253 arrives on the timetable: more than half a day, so not a connection we count.