First off what is the recipe and how long does the frosting have to sit before they cookies would be ready to be served?
I'm sorry, I'm confused. Do you mean what is a recipe for royal icing? And how long does it have to set before eating?
I would assume it can be eaten any time - though you might want to wait until it's solid so it doesn't make a mess! If I'm stacking and transporting my decorated iced cookies, I try to wait 24 hours. But, if they aren't being stacked I don't think you have to wait that long. DEpending on how thick or thinthe icing is, the drying time will vary.
I think there are recipes in the recipe section here. I have a recipe that calls for 2 pounds powdered sugar, 3 tablespoons meringue (sp?) powder and 5-6 tablespoons warm water (or more depending on how thin you want it to be). But I love the recipe Antonia74 suggested in her tutorial.