You should know that the sweet spot for YC founders is a team with at least one person capable of building the product, and that the competition includes folks who once had a very good idea but, as of the time of application or their interview, possess a working prototype of the idea which they have begun to expose to market feedback. In many cases, they will already have revenue, sometimes meaningful revenue.
If you want to get into YC, I would advise taking whatever steps are presently possible to create the business, and then demonstrating that you're making forward progress when you apply. Happily, this is exactly what you'd try to do if you weren't trying to get into YC, so it shouldn't be a major imposition.