UA 3909 then TK 9591 at San Francisco
Chicago O'Hare → San Francisco → Las Vegas
Timetable, San Francisco time
22:20UA 3909 from Chicago O'Hare at the gate
19:00TK 9591 to Las Vegas leaves the gate
20 h 40 apart on the timetable, overnight
TK 9591 leaves 20 h 40 after UA 3909 arrives on the timetable: more than half a day, so not a connection we count.