I've never heard of this percentage, but I suspect that such a recommendation does exist.
However, I doubt that it is very useful as that would just be a mean, or median. All conures are different, they should be fed enough to maintain a healthy weight and their diet should be adjusted as needed.
Most conures are pretty good at regulating their own diet (they eat when they're hungry) as long as you provided them a healthy selection of foods.
A good pellet food should be their primary food (Zupreem, Harrisions, etc). This should be supplemented with fresh fruits and veggies. It's also good to mix in some variety: a bit of egg here or there, maybe a nibble of chicken; this is easiest by sharing whatever you are eating if it is healthy.
I keep Auggie's pellet bowl stocked all the time. He also has another bowl in his cage where I mix any other dry (aka non-perishable) goodies that I might give him such as some freeze dried veggies, nuts, etc. Generally he only gets his fresh foods while I am here - mostly at dinner time.
