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.