When do you know it's the right time to stop outlining and start writing your new work in progress?
I wish there was a better answer for you, but that's the reality about writing. There's no tried and true formula to it, and yet it's a question that pops up quite frequently. You don't really ever know when it's the right time to start writing until you actually start writing.
With every project I've written, the process has been different. Some have started with a hot impulse to write a small passage or a chapter. Others have come to me from a dream. Ideas have grown from seeds drawn from another book or movie or even a song. Only once have I started a project with an outline. Never have I written an entire outline before I started writing.
One of the things that has held true for me is that there's a volley between outlining and writing. I'll start outlining, get to a point to where I feel like I'm stuck or burned out or just eager, and then I'll start writing. It might only be a chapter, or it could be a dozen, before I end up taking a step back and return to my outline.
"Outline" becomes an ambiguous term at that point. After writing, there are things I discover about my characters, themes, and plot that I would not have found had I committed to finishing an outline. What my outline becomes is a collection of all these ideas that I expand on, and research, and then I continue my writing. Eventually, my outlines become more like foundational guides to keep me grounded the deeper I get into the narrative.
This formula works. For me.
I would not have found what worked for me had I not experimented. I tell everyone this when they ask about when to outline and when to write: experiment.
One of the biggest mistakes people make when they are working on a new project is that they expect perfection. We have huge fears of running into writer's block. We worry that no one is going to read it, or what we write is going to be terrible. We spend so much time trying to avoid all these things that we end up in outline limbo. We keep ourselves from getting started, and often, that's what an outline ends up being.
Your first draft is going to suck. And that's fine. The first attempts at any chapters are going to be imperfect. But you're figuring it all out as you go along. You'll have the chance to revise your writing. You'll also revise your outline.
Trust yourself, though. When you feel stuck, try something different. Nothing is ever perfect. Getting close to perfection takes time, trial, and error. Know that you'll never be 100% ready for something, and that each project is different from the last.
...and Happy Outlining!