UA 3909 then OZ 9521 at San Francisco
Chicago O'Hare → San Francisco → Houston
Timetable, San Francisco time
22:20UA 3909 from Chicago O'Hare at the gate
16:40OZ 9521 to Houston leaves the gate
18 h 20 apart on the timetable, overnight
OZ 9521 leaves 18 h 20 after UA 3909 arrives on the timetable: more than half a day, so not a connection we count.