KE 23 then UA 3906 at San Francisco
Seoul → San Francisco → Washington
Timetable, San Francisco time
09:35KE 23 from Seoul at the gatealso DL 7860
07:00UA 3906 to Washington leaves the gate
21 h 25 apart on the timetable, overnight
UA 3906 leaves 21 h 25 after KE 23 arrives on the timetable: more than half a day, so not a connection we count.