UA 876 then B6 1034 at San Francisco
Tokyo Haneda → San Francisco → Boston
Timetable, San Francisco time
11:15UA 876 from Tokyo Haneda at the gatealso NH 7010
06:00B6 1034 to Boston leaves the gatealso EY 8006, EY 8261
18 h 45 apart on the timetable, overnight
B6 1034 leaves 18 h 45 after UA 876 arrives on the timetable: more than half a day, so not a connection we count.