AS 279 then AA 3748 at Boston
Seattle → Boston → Washington National
Timetable, Boston time
18:00AS 279 from Seattle at the gate
07:30AA 3748 to Washington National leaves the gate
13 h 30 apart on the timetable, overnight
AA 3748 leaves 13 h 30 after AS 279 arrives on the timetable: more than half a day, so not a connection we count.