[kemayo]

Since it sounds like you're asking when you should quit to focus on a startup... to avoid potential legal troubles, the answer is before you started working on the startup (or certainly before you launched the startup). Ergo it's when you've got enough saved up to support working until you think you'll make income / get funded.

Otherwise, if you don't care about the legal / ethical risk, I'd say that you need to make a decision about where to focus once the startup is consuming enough effort that it's crowding your life.