When does green (nitrogen) material turn to brown (carbon) material?

A good compost is what, 1 part green to 3 parts brown material, or something like that? Suppose I rake up some freshly fallen leaves. These are green with lots of nitrogen. Now I also have a pile that I made 2 months ago. They are all dried up and and crumbly. These are brown and have little nitrogen and are mostly just carbon. Am I right so far? Now here is my question. How long does the green pile take to become like the brown pile? How long is the green pile usable as nitrogen and when does it become usable as carbon?

As with most permaculture answers, it depends.  As those greens dry, the nitrogen gasses off.  So it depends upon heat and humidity, air flow and the relative moisture level of the greens to start.