AA 3744 then DL 1399 at Boston
Washington National → Boston → Miami (MIA)
Timetable, Boston time
12:10AA 3744 from Washington National at the gate
07:15DL 1399 to Miami (MIA) leaves the gate
19 h 05 apart on the timetable, overnight
DL 1399 leaves 19 h 05 after AA 3744 arrives on the timetable: more than half a day, so not a connection we count.