A safe play, quit when the company is actually cash-flowing and can replace your current salary/benefits, etc. Founders running out of personal cash is an all too common pitfall.
Very often founders underestimate how much hard work, resources, and calendar time are required to make their company successful. They also overestimate the absolute value of the return. Typically, building a revenue stream is a slow organic process that takes quite a while until it can support one, not to mention several, co-founders.
If you have a cash buffer, go ahead and quit your job. But even then, don't do it without a plan of how much time (or how much of that buffer) you're ready to spend on your startup. Be specific.
Unless you can already smell money, accept that you will make 0 for months to years. And then you'll be making chump change for more months to years. Can you afford this?