AA 873 then UA 3872 at O'Hare
Atlanta → Chicago → LCQ
Timetable, Chicago time
12:29AA 873 from Atlanta at the gate
00:31UA 3872 to LCQ leaves the gate
12 h 02 apart on the timetable, overnight
UA 3872 leaves 12 h 02 after AA 873 arrives on the timetable: more than half a day, so not a connection we count.