UA 1251 then CA 3174 at O'Hare
St Louis → Chicago → Guangzhou
Timetable, Chicago time
20:19UA 1251 from St Louis at the gate
17:25CA 3174 to Guangzhou leaves the gate
21 h 06 apart on the timetable, overnight
CA 3174 leaves 21 h 06 after UA 1251 arrives on the timetable: more than half a day, so not a connection we count.