AA 866 then UA 3907 at O'Hare
Boston → Chicago → Cleveland
Timetable, Chicago time
15:37AA 866 from Boston at the gate
07:30UA 3907 to Cleveland leaves the gate
15 h 53 apart on the timetable, overnight
UA 3907 leaves 15 h 53 after AA 866 arrives on the timetable: more than half a day, so not a connection we count.