I have the same setup on my trainer and had the same question. After a few dead sticks under my belt, I took it up and set her to wide open and started the clock. I think I got just under 15 minutes. Flying at half throttle, I am sure you can get a fair bit longer but without much difference in speed. I hope this helps.

As for deadsticks, they are really no big deal if you are over the field. Just keep it over the field doing circles. When the engine quits, fly your approach. That plane floats!!

Zee