SQ 1539 then BA 2947 at San Francisco
Boston → San Francisco → Seattle
Timetable, San Francisco time
00:25SQ 1539 from Boston at the gate
17:42BA 2947 to Seattle leaves the gate
17 h 17 apart on the timetable
BA 2947 leaves 17 h 17 after SQ 1539 arrives on the timetable: more than half a day, so not a connection we count.