AA 9909 then UA 1653 at O'Hare
Waterloo → Chicago → Las Vegas
Timetable, Chicago time
17:10AA 9909 from Waterloo at the gate
14:30UA 1653 to Las Vegas leaves the gate
21 h 20 apart on the timetable, overnight
UA 1653 leaves 21 h 20 after AA 9909 arrives on the timetable: more than half a day, so not a connection we count.