Well the hour is off the 250cc tank fill up bottle on my 1/10th scale HPI MT1.9(MT1 heavily modded with MT2 parts), which has a 75CC tank that I can easily fill up 4 times and each tank lasts 15-20 mins with a nitro star t-15 engine(not a speed demon but it hits around 32-35 MPh which is perfectly suitable for bashing). A gallon of nitro fuel can easily keep it goin for over 12 hours. (side note I find the NitroStar T-15 extremely easy to tune, keep the tune, and highly reliable)
Now my savage X is a quite a bit more nitro hungry with its 4.6 and gets around 15-20 mins for a 160CC tank. It eats through Nitro at a little over 2X my MT1.9 but hell it is like 5X the fun though
But still I can keep it going as long as I got a nitro with a few seconds of downtime in between tanks. no pre-planning how long you want to run and how many batteries to charge. (unlike most I use AA's in my nitro's RX's so no pre-planning even there) When I usually run my nitros I usually run till my arm starts hurting from holding the controller
when i run my nitro cars and truck i always use u the whole gallon of fuel every time i start the engine i drive and bash them the whole time i re fuel when the tanks get real low and i just refuel while the engine is running so i never have to re start the engine and they just keep going and going most time i end ready to bring them end because i been had so much fun that it be too dark to see em