AA 642 then UA 2811 at O'Hare
Dallas-Fort Worth → Chicago → Las Vegas
Timetable, Chicago time
13:10AA 642 from Dallas-Fort Worth at the gate
09:00UA 2811 to Las Vegas leaves the gate
19 h 50 apart on the timetable, overnight
UA 2811 leaves 19 h 50 after AA 642 arrives on the timetable: more than half a day, so not a connection we count.