[philomath_mn]

There are some ebbs and flows, but usually everything is happening all at once. There is usually never a single product, and even then different parts of a product will be in different stages at the same time.

So you could be doing heavy prototyping or feature work on a mature product if you are enhancing it in some way, or you could be doing some maintenance / refactoring / bug-fixes on an early stage product.

The distribution of time between those tasks will change over the life of the product, but there is rarely a "feature complete" stage in my experience.