Rustoleum will get pretty hard if allowed to cure completely. I have had best luck with a single, wet coat. Trying to dust on a coat to save weight is not the way to do this paint. It is not dope and not lacquer. You don't want to rub it out, you want the skin of the paint intact. I suspect that has a lot to do with its fuel resistance.
It will also depend on just how thick you put it on. It takes time for the volatiles to migrate out of the paint, and the thicker the film, the longer it takes. And cold temps slow that down as well. So I'd be wary of a real specific answer that works perfectly of Joe Perfect Painter. He probably put exactly the right amount on with no thick areas. Probably in his well-lighted paint booth, that just happens to be in a temp controlled building--which also controls the humidity. For the rest of us, we make do as best we can.
And actually, since models are lightweight and flexible, you don't want a paint that is super-hard--because that makes them brittle. and cracks are going to happen. Putting the paint over a glass-epoxy layer helps a lot. Just putting it over a brush-coat of epoxy like EZ-Lam helps a lot. I learned this on a solid-wing model that I just sanded and went to Rustoleum Automotive Primer and then topcoated. Looked good for a year or so, then paint checking started span-wise. Ok, that was a very easy paint method, but not good enough even for quick and dirty. Maybe good enough for quick and crash airplanes. I try not to build those.
I would let Rustoleum cure at least a week before getting fuel on it, if you want to avoid softening the surface and likely affecting its durability. Personally, I try to set the plane out in the sun for a few days after it has 12-24 hours of cure time. This seemed to help a lot. I have also put a plane inside my truck in the winter to try to ensure a full cure.
If applied well, over good surface prep, and given a "forced cure," the biggest remaining liability of Rustoleum on the ones that I have done is bubbling. This occurs when the paint skin is intact and still fuel-resistant, but fuel has been allowed to creep underneath causing it to bubble or blister. This mostly occurs on the fuselage near a landing gear hole or other place the paint isn't acting as a complete barrier. This is of course one of the hardest things to solve on a model regardless of paint type. So much so that really skilled modelers that were fed up with the problem just started molding composite parts with no balsa in them.
I found Rustoleum to be miles ahead of LusterKote, but not as good as KlassKote. For sport models and quick builds it is pretty good stuff. For electrics I imagine it has even fewer liabilities.
Good luck with your paint jobs!
Dave