UA 3905 then UA 2256 at Houston
Cancún → Houston → Monterrey
Timetable, Houston time
13:29UA 3905 from Cancún at the gate
10:10UA 2256 to Monterrey leaves the gate
20 h 41 apart on the timetable, overnight
UA 2256 leaves 20 h 41 after UA 3905 arrives on the timetable: more than half a day, so not a connection we count.