UA 6259 then UA 3907 at Houston
Knoxville → Houston → Washington
Timetable, Houston time
08:40UA 6259 from Knoxville at the gate
07:00UA 3907 to Washington leaves the gate
22 h 20 apart on the timetable, overnight
UA 3907 leaves 22 h 20 after UA 6259 arrives on the timetable: more than half a day, so not a connection we count.