A question about a recipe: Zucchini Risotto with Stuffed Squash Blossoms

I have a question about the ingredient "zucchini flowers with stems" on the recipe "Zucchini Risotto with Stuffed Squash Blossoms" from SarahMK.

At what point in the life of a zucchini blossoms is it best to harvest? In other words, what should the blossoms look like at harvest peak.