In some cases, InFlightInfo may indicate a departure time of the first received position, if it hasn’t received a message from the airline announcing an actual departure time. You can use FlightInfoEx to retrieve times that should correspond more closely with the website.
In the case of that VIR26 flight, we began receiving the first position information earlier than the departure time that was eventually reported to us through other sources. If you look at the track log for that flight, you can see that this is because there are ground positions being reported to us as the flight is taxiing on the airport surface: flightaware.com/live/flight/VIR2 … L/tracklog
first_position | 2013-06-21 11:27:37 UTC
filed_departuretime | 2013-06-21 11:20:00
estimateddeparturetime | 2013-06-21 11:44:00
actualdeparturetime | 2013-06-21 11:43:00