UA 1580 then B6 1187 at Boston
Chicago O'Hare → Boston → Los Angeles
Timetable, Boston time
16:11UA 1580 from Chicago O'Hare at the gate
15:45B6 1187 to Los Angeles leaves the gate
23 h 34 apart on the timetable, overnight
B6 1187 leaves 23 h 34 after UA 1580 arrives on the timetable: more than half a day, so not a connection we count.