UA 3913 then AC 580 at Houston
Denver → Houston → Montréal
Timetable, Houston time
21:22UA 3913 from Denver at the gate
11:50AC 580 to Montréal leaves the gate
14 h 28 apart on the timetable, overnight
AC 580 leaves 14 h 28 after UA 3913 arrives on the timetable: more than half a day, so not a connection we count.