With just a pound it probably doesn't matter, but if you ever need to add more than that in the future I'd double check the IBU math, especially if you're doing a partial boil. If the recipe thought you were adding at the beginning and you didn't, the gravity when you add your boiling hops would be lower and you'll wind up with higher IBUs. I definitely turned an APA into an IPA by adding some extract later and not thinking about it, and I'd think the same would apply to table sugar.