B6 778 then B6 455 at Boston
Las Vegas → Boston → Washington National
Timetable, Boston time
06:32B6 778 from Las Vegas at the gate
06:10B6 455 to Washington National leaves the gate
23 h 38 apart on the timetable, overnight
B6 455 leaves 23 h 38 after B6 778 arrives on the timetable: more than half a day, so not a connection we count.