UA 3922 then AA 3768 at O'Hare
Savannah → Chicago → St Louis
Timetable, Chicago time
02:36UA 3922 from Savannah at the gate
20:59AA 3768 to St Louis leaves the gate
18 h 23 apart on the timetable
AA 3768 leaves 18 h 23 after UA 3922 arrives on the timetable: more than half a day, so not a connection we count.