AA 3258 then UA 3907 at Houston
Miami → Houston → Chicago
Timetable, Houston time
09:00AA 3258 from Miami at the gate
12:00UA 3907 to Chicago leaves the gate
3 h apart on the timetable
The last days
AA 3258 and UA 3907 weren’t both flown 15 min to 12 h apart in the last 21 days.
Statistics from past flights, not live flight information. Always check times and your connection with your airline, and don’t base travel or booking decisions on these numbers.