UA 3913 then UA 2144 at Houston
Denver → Houston → Jacksonville
Timetable, Houston time
21:22UA 3913 from Denver at the gate
13:19UA 2144 to Jacksonville leaves the gate
15 h 57 apart on the timetable, overnight
UA 2144 leaves 15 h 57 after UA 3913 arrives on the timetable: more than half a day, so not a connection we count.