When you create a novel, there is a certain amount of time and money you will need to invest. Some of the time of composing the book is easy to gauge, but other allocations are harder to see.
Brainstorming and outlining your story. This is something that normally takes a few days, at least. You may want to write out your ideas, talk with your writing group, and run it past an editor or agent. I often have authors who have me “greenlight” their outlines as they look for ways to tell a story better or adapt it to a larger audience (email email@example.com to set up appointments to do that). So outlining might take a few days, but I’ve seen authors spend weeks honing a good outline to perfection.