AA 4912 then UA 2210 at LAX
St Louis → Los Angeles → Boston
Timetable, Los Angeles time
10:37AA 4912 from St Louis at the gate
22:45UA 2210 to Boston leaves the gate
12 h 08 apart on the timetable
UA 2210 leaves 12 h 08 after AA 4912 arrives on the timetable: more than half a day, so not a connection we count.