DL 400 then AA 3748 at Boston
San Francisco → Boston → Washington National
Timetable, Boston time
15:45DL 400 from San Francisco at the gate
07:30AA 3748 to Washington National leaves the gate
15 h 45 apart on the timetable, overnight
AA 3748 leaves 15 h 45 after DL 400 arrives on the timetable: more than half a day, so not a connection we count.