I am sorry but you dont understand how it works. The most work is programming, writing (plot, dialogs) and setupping scene (animation, pose). Time spend for computer render an image is not a work and does not double development time, You dont even need to sit in front of computer during render. Also You can code or write plot during image render. To be shaved or not is just a toggle which takes few secconds to apply and render second image. You render first image then press toggle to enable hair, render second image and you can cut extra image area which is equal with first image, that allow to save disk space, just put hair as a second layer to first (shaved) image.
You could also probably setup software not to render other duplicate area since you dont need it for second image.