AA 642 then UA 1606 at O'Hare
Dallas-Fort Worth → Chicago → Boston
Timetable, Chicago time
13:10AA 642 from Dallas-Fort Worth at the gate
10:30UA 1606 to Boston leaves the gate
21 h 20 apart on the timetable, overnight
UA 1606 leaves 21 h 20 after AA 642 arrives on the timetable: more than half a day, so not a connection we count.