I harvest giant sunflowers on a “biodynamic flower day” when most of the yellow petals have dropped off. I rub off the florets, clear off all insect and any otherwise damaged seeds (chickens love them) with a pocketknife then allow the head full of seeds to dry in the sun without removing them from the flower head.
I store them that way as well once the flesh of the flower has dried up completely. My favorite way to eat them are as micro greens. I save the “best” and biggest seeds as well as by certain colors... I am just starting to select for giant single-headed sunflowers that only grow under 6 feet tall so I can better observe the developing flower, which has an incredible fragrance as it grows to maturity (which explains why bees love ‘em) and much less likely to be blown over by the wind... We have dogs on the property that keep the deer away.