UA 4989 then UA 3907 at Houston
Mobile → Houston → Washington
Timetable, Houston time
10:50UA 4989 from Mobile at the gate
07:00UA 3907 to Washington leaves the gate
20 h 10 apart on the timetable, overnight
UA 3907 leaves 20 h 10 after UA 4989 arrives on the timetable: more than half a day, so not a connection we count.