AA 642 then UA 3556 at O'Hare
Dallas-Fort Worth → Chicago → St Louis
Timetable, Chicago time
13:10AA 642 from Dallas-Fort Worth at the gate
08:55UA 3556 to St Louis leaves the gate
19 h 45 apart on the timetable, overnight
UA 3556 leaves 19 h 45 after AA 642 arrives on the timetable: more than half a day, so not a connection we count.