SQ 1539 then UA 2091 at San Francisco
Boston → San Francisco → Chicago O'Hare
Timetable, San Francisco time
09:40SQ 1539 from Boston at the gate
06:35UA 2091 to Chicago O'Hare leaves the gatealso AC 5366, NZ 9309
20 h 55 apart on the timetable, overnight
UA 2091 leaves 20 h 55 after SQ 1539 arrives on the timetable: more than half a day, so not a connection we count.