At what point should I make the full leap from my day job to my startup?
You have to deal with your gut.
Also, consider your situation. How deeply are you in debt? How much do you and anybody else depend on your income? Do you have a strong family that can serve as a safety net? If you're young and unattached you can probably take more risk than if you're already on the edge of debt and supporting others.
If it's any consolation to you, you have a lot of company.