LA 6139 then UA 1 at San Francisco
Boston → San Francisco → Singapore
Timetable, San Francisco time
23:58LA 6139 from Boston at the gate
22:40UA 1 to Singapore leaves the gate
22 h 42 apart on the timetable, overnight
UA 1 leaves 22 h 42 after LA 6139 arrives on the timetable: more than half a day, so not a connection we count.