AA 4639 then DL 1428 at JFK
Boston → New York → Miami
Timetable, New York time
07:30AA 4639 from Boston at the gate
19:40DL 1428 to Miami leaves the gate
12 h 10 apart on the timetable
DL 1428 leaves 12 h 10 after AA 4639 arrives on the timetable: more than half a day, so not a connection we count.