That has a very variable answer.
How quickly you can build traffic, is your static, or RSS fed site going to make people want to return, or recommend your site. How many sites you are doing is another thing. Is your SEO work going to keep it in a good position, or will a new black hatter run you to ruin? What is, or are, your niche(s) and is it, or they, going to draw enough traffic to make it worthwhile.

A lot depends what you are doing, for the length of time it could take, and some have spent a lot of time doing things wrong and never have achieved much.