AA 2556 then UA 3376 at O'Hare
San Diego → Chicago → St Louis
Timetable, Chicago time
19:59AA 2556 from San Diego at the gate
11:00UA 3376 to St Louis leaves the gate
15 h 01 apart on the timetable, overnight
UA 3376 leaves 15 h 01 after AA 2556 arrives on the timetable: more than half a day, so not a connection we count.