UA 3901 then TP 4392 at San Francisco
Los Angeles → San Francisco → Boston
Timetable, San Francisco time
09:36UA 3901 from Los Angeles at the gate
22:10TP 4392 to Boston leaves the gate
12 h 34 apart on the timetable
TP 4392 leaves 12 h 34 after UA 3901 arrives on the timetable: more than half a day, so not a connection we count.