The longer you can wait, the better. Your idea will be better developed. You’ll have more feedback from the customers that you’re discussing the business with, and generally speaking, when you have those elements you’re much more likely to be successful in raising funding.
Another dimension of it is that venture capitalists generally prefer to write larger checks, that’s the nature of what they do and your capital needs as you grow a business are going to increase as you scale it.
So, venture capitalists are a much better target once you’ve matured the idea, you understand what customers in the market think of what you’re doing, and you need the resources to just scale that business.