Hello ... I've pivoted a few times and can tell you that the answer to your question is not binary. There is no answer to your question based on time, quantity of customer interviews, or even a sales figure.
Sorry to say this, but I don't think that this question will really get you the answers you're looking for.
If your challenge is that you feel that you've put in enough "time" and, hence, think you can start to pivot your model to the next phase - you're looking at it the wrong way.
If you've managed to start-up and align the company along your mission, vision and values ... then the key is to hone in on the sweet spot. That 20% of your customers, contacts, employees, etc that drive 80% of your results. You need to refine your model to a sustainable competitive advantage that is a beacon to the customers you want, the employees you need, and the resources to bring them all together.
You turn on the light and become that beacon when you start to build organizational alignment around mission, vision, and values. The key is then based around getting the Right People in the Right seats and working on the Right things. Suggest you read the Rockefeller Habits by Verne Harnish if you haven't already.
You can focus on your BHAG, but keep the focus on the next step. You can focus on innovation and marketing in that space and that's where the company needs you.
If you want to go fast, go alone. If you want to go far, you need to bring people with you ...
When you've built the systems and structure around alignment you're ready to pivot and scale.
I have lots of blog posts on this subject, just follow this link: http://wisenapkin.com/tag/growth/
Make it a great day!
