AA 642 then UA 1580 at O'Hare
Dallas-Fort Worth → Chicago → Boston
Timetable, Chicago time
13:10AA 642 from Dallas-Fort Worth at the gate
12:46UA 1580 to Boston leaves the gate
23 h 36 apart on the timetable, overnight
UA 1580 leaves 23 h 36 after AA 642 arrives on the timetable: more than half a day, so not a connection we count.