AA 4778 then DL 811 at Houston
Philadelphia → Houston → Miami
Timetable, Houston time
13:55AA 4778 from Philadelphia at the gate
15:25DL 811 to Miami leaves the gate
1 h 30 apart on the timetable
The last days
AA 4778 and DL 811 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.