Depends - Truggy or buggy, fuel, pipe, trigger finger, driving style, tune, ambient conditions.

With a 6.5 mm restrictor, 25% fuel, nice smooth driving style on a grippy track with a good tune - you should get 9 - 10 min in a buggy (ha, talking about the perfect world again ). Truggy expect a little more under the same conditions.
There are so many variables that's about as close as you will get to an accurate answer I reckon. You will always get the freak conditions that give someone a 12 min tank, likewise the bad days when you can only get 7 1/2 min no matter what you try.