422 is SEA-DEN arriving around 4 am and 522 is DEN-CLE departing around 2 pm. Most airlines try to avoid scheduling similar flight numbers to the same city at the same time but delays can happen and mess up the best of plans. Different airlines also can have similar flight numbers at the same city at the same time. Pilots and air traffic controllers are also used to listening up and ATC will issue a warning to a flight if another flight with a similar callsign is on the same frequency at the same time.