AA 3523 then UA 3755 at O'Hare
Baltimore → Chicago → Denver
Timetable, Chicago time
12:59AA 3523 from Baltimore at the gate
18:37UA 3755 to Denver leaves the gate
5 h 38 apart on the timetable
The last days
AA 3523 and UA 3755 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.