AA 9950 then UA 646 at O'Hare
Philadelphia → Chicago → Denver
Timetable, Chicago time
13:49AA 9950 from Philadelphia at the gate
13:30UA 646 to Denver leaves the gate
23 h 41 apart on the timetable, overnight
UA 646 leaves 23 h 41 after AA 9950 arrives on the timetable: more than half a day, so not a connection we count.