I have had the pleasure of working with a great client recently that has been very successful. He's the ultimate entrepreneur who flies by the seat of his pants. It suddenly became apparent that he could not translate how he did what he did in a way that someone else could duplicate. Also, not everyone liked that approach. They were looking for a little bit more direction. It is really neat to be able to help his company not only reign in the vision, articulate it and then share it with the group. We are also documenting the process so it is no longer subjective or in the head of just one person. This will be something anyone can plug into.
So the question becomes "when is it time to document?" My answer is now and always. Even when it's just you, if you think you ever want to grow your business or more importantly, some day sell the business, it has to be documented. If it is not documented, you do not have a business with out the source, the owner. If you don't document, and the source is not available, the business stops. So by all means document the process.