There is no better time than now.

If you have already done the customer validation and figured out your value prop then the next step would be to build a quick and dirty landing page on something like instapage or leadpages, direct people/testers to this page, and make sure that your copy is clear, the benefit/value prop is easily understood, and that your main CTA is making sense.

At the same time, since you are building your clickable prototype (I assume on a tool like invision), take the same user tester through your 'mock app' and get their feedback.

One you've done this at least ten times (you should be able to do this in a day), you are ready to get a pre-registration page up, direct some traffic to it, and hopefully see people request early access to your tool. this will buy you some time to get your app up and running. And believe me when I say this, it does not have to be perfect right now, just needs to work and solve the pain you've identified already.

You should also look at bolting a tool like Intercom on the backend of your app to guide your new users, provide them a quick visual tour, and collect their early feedback.

Like Elon Musk says, be bold, take risks, expect to fail but do it anyways.

Best of luck!
- Loic