Based on what I’ve seen from other users, waiting a few days (3-4) would be ideal, without counting weekends. If it’s for your first paid project, a bit of extra time is required.
If after all this wait your project is still not indexed, it sounds like something else might be wrong. Maybe you haven’t set up your profile correctly, maybe you missed something, maybe the review queue is just too busy.
If you market your project outside of Itch, people should still be able to access your project, even if it’s not indexed, so hopefully that won’t be impacted by when it will be indexed.