Personally, when I'm building side projects I spend 100% on dev for the first month. then when it's released I spend 90% of the time on marketing.
Anyone can code up a project or learn how to do it. The hardest part is getting word out to others. Even, just getting people to try it takes huge amounts of time and effort and money. Often times it seems like it takes more marketing work than development work.
For instance, I've been helping people prevent bugs in their code with my Regression testing platform: https://swif.club/?s=h2
But, doing so without seeming spammy takes a lot of time and patience.