Nope. You don't have to wait. If you happen to app an Eddie Brock before there's a Peter Parker, the only thing that matters is if your app meets the qualities we're looking for. 

What I'm saying is, if there is already a Peter Parker, a Miles Morales, a Cindy Moon, and then someone apps an Eddie Brock, it'll be much more difficult for that Eddie Brock app to be accepted at that point out of oversaturation concerns. That doesn't mean you need to wait to see what's around first. Like I said, this isn't a fresh world so there's plenty of room for legacies to be around without parent characters. 

That being said, I would be shocked if a Spider-Man app wasn't submitted within ten hours of an OOC going up.