DL 5740 then DL 1599 at Boston
Philadelphia → Boston → Washington National
Timetable, Boston time
07:31DL 5740 from Philadelphia at the gate
20:05DL 1599 to Washington National leaves the gate
12 h 34 apart on the timetable
DL 1599 leaves 12 h 34 after DL 5740 arrives on the timetable: more than half a day, so not a connection we count.