Departure Time reporting inconsistant Southwest vs Airtran


Why are Airtran departure times being reported a good 10-15 minutes BEFORE they are in the air at 900 feet?


It takes them a long time to climb?




IT is being shown as departing ATL at 10:15 PM EST but there are no flight data points (coordinates and altitude) until 10:43 PM EST. This time is was 28 minutes.