My guess would be 6 minutes give or take. I normally set my DX7 timer for 6 minutes for the same battery and my Trex 450 Sport. You are not running hard, so your flight would probably be a bit longer. Your charger might be able to tell you what the voltage is after flight. If they are newer batteries, they will also last longer. If you could calculate the Amps your motor is drawing, you could calculate the time more accurately.