UA 3909 then UA 1971 at San Francisco
Houston → San Francisco → Chicago O'Hare
Timetable, San Francisco time
07:17UA 3909 from Houston at the gate
22:45UA 1971 to Chicago O'Hare leaves the gatealso AC 4200, AC 5432, NZ 9303
15 h 28 apart on the timetable
UA 1971 leaves 15 h 28 after UA 3909 arrives on the timetable: more than half a day, so not a connection we count.