I would like to share our last experience. It is a flight of 3 hours and 35 minutes in hover. It is our longest flight so far, the flight is an internal test in which we did not plan to fly so long. In fact we had 400gr of extra weight that could have been removed and the fuel tank was not full at all. We take off with 5 liters but it is possible to fill 5.2 liters or so.
The relevant thing for us is that this unit is a "stock" aircraft, we have not made any modifications, lightening or additional fuel tanks to do this test, the maximum flight time of the aircraft should be about 4 hours, obviously without any payload. I think that in normal operation flight times should be between 2 and 3 hours.