WN 209 then UA 588 at Denver
St Louis → Denver → Houston
Timetable, Denver time
18:50WN 209 from St Louis at the gate
16:44UA 588 to Houston leaves the gate
21 h 54 apart on the timetable, overnight
UA 588 leaves 21 h 54 after WN 209 arrives on the timetable: more than half a day, so not a connection we count.