DL 3968 then DL 438 at Seattle
Vancouver → Seattle → Boston
Timetable, Seattle time
16:53DL 3968 from Vancouver at the gate
11:45DL 438 to Boston leaves the gate
18 h 52 apart on the timetable, overnight
DL 438 leaves 18 h 52 after DL 3968 arrives on the timetable: more than half a day, so not a connection we count.