UA 3905 then B6 1734 at San Francisco
Tokyo Haneda → San Francisco → Boston
Timetable, San Francisco time
16:33UA 3905 from Tokyo Haneda at the gate
10:44B6 1734 to Boston leaves the gatealso FI 7830
18 h 11 apart on the timetable, overnight
B6 1734 leaves 18 h 11 after UA 3905 arrives on the timetable: more than half a day, so not a connection we count.