When I play with my OS .46 AXI powered NextStar just shooting touch-n-go's, I'll get close to 30 minutes and have fuel left over. Of course, I'm also using only 1/2 throttle on the take-off, keep the pattern tight by not flying out more than 150', keeping the altitude to 50' and cutting the throttle to idle when the plane is directly across from me and glide with a very tight pattern and land directly in front of myself. Under normal flying and using it to train people, I'll fly at 1/2 to 2/3 throttle and can get around 20 minutes if the student is doing good. Most likely the student will start to tire in about 10 to 15 minutes, then it's time to land with plenty of fuel remaining.

Hogflyer