Presumably much of the information here (and in other places) comes from Flightradar24. I've been wondering about their accuracy for a while, in particular wondering just what they use as their departure times. Looking back at a couple of my flights, I've found substantial differences between their times, and my own. For instance, on my last flight, we departed 1 minute early, and yet FR24 shows departure as 15 minutes late. Fairly obviously, they're not using the departure time (which is recorded at the gate), but rather the airborne time (though I can't even make that fit on all occasions).