I don't really understand why scripting is so tied to renders. Why can't you use placeholder images, which are a sketch or text of the future content of the render? Thus, you can safely prepare all the scripts and even conduct testing with catching bugs long before the end of rendering. And as the renders are ready, replace the placeholder images with them.
Moreover, this will allow you to more accurately predict the release date, since having completed and debugged script, it remains only to measure how many renders can be done per day on average, and based on this, calculate how many days it takes to render all the necessary images.