UA 4523 then UA 3907 at Houston
Huntsville → Houston → Washington
Timetable, Houston time
08:40UA 4523 from Huntsville 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 4523 arrives on the timetable: more than half a day, so not a connection we count.