I am amazed every year by how rapidly the nuts begin to grow after the ovary is fertilized.  The bees and pollen have done their job so it's "off to the races".

In this picture we have blossoms still blooming, blossoms with fallen petals, nutlets just breaking their jackets (the calyx), and nuts from which the jacket has fallen.
Just after jacket-split is the most frost sensitive time for the nutlet.