AA 1260 then UA 3376 at O'Hare
Boston → Chicago → St Louis
Timetable, Chicago time
18:55AA 1260 from Boston at the gate
11:00UA 3376 to St Louis leaves the gate
16 h 05 apart on the timetable, overnight
UA 3376 leaves 16 h 05 after AA 1260 arrives on the timetable: more than half a day, so not a connection we count.