I will not promote - when’s the right time to quit my high paying job?

I will not promote Working for a top tech company which has many products. I am planning to build a startup that’s in the same space but it’s not a direct competitor. I have a plan to launch it in the next 3-4 months. Question is when is the right time to quit? The problem is that I am solving an area that the current company is not focusing on. But I can imagine if we are wildly successful, my company would potentially want to even buy the product. (Yeah I know I am getting carried away here). But I can’t dismiss that microscopic possibility. I am working on personal computer, and never in the office. I also don’t go to the office much, that’s another story. I don’t have a concept of company time because in big tech, the hours are so random and flexible. I am not going to disclose the idea to my company or sign a non-compete as I don’t want to. I have to keep this in wraps until I launch. I don’t want to deal with any possible legal lawsuits demanding the work I have is from the company. It’s obviously not stolen because I am building something new. - should I quit now before the work even begins? - should I wait 1 month before launch? - should I wait till 1 week before launch? - should I just keep at it until mvp is proven??