I have flewn A3 865 PRG-ATH recently and the flight was 1 hour delayed. No big deal for me but I thought I should have received the free ticket letter that has been mentioned on the forum. I went on and asked A3 CS. This is what I have received in reply:
We confirm that the above mentioned flight delayed to depart by fifty three (53) minutes. The reason of the delay was the late arrival of the incoming aircraft.
We offer a fare free ticket to our passengers, whose international flight departed with a total delay of more than two (2) hours or whose domestic flight departed with a total delay of more than one hour. At this point, we would like to mention that this offer is applied, as a goodwill gesture, in cases that the delay caused due to our responsibility.
So it is 1 hour on domestic and 2 hours on international.