How many times have you heard at dinner, "I would like to write a book someday" or "I hope to be finished in a year or so." Sound familiar? I took one month off to finish my second, yes, second in the series, ALLOUETTE, "STRONGER TOGETHER." I started Jan 1 and finished Apr 30. I took off my writer's hat and have moved to the editing phase. After that, the dreaded marketing phase.
I spent a year in R&D, with a writing start date of Jan 1 and an end date of May 1. My suggestion is to treat it like a contract with yourself. Have a start date. Have an end date. Break it down not just into years, but months and weeks. I have a big white board I filled out the day I started. Subject to change, of course. When you personally see progress, it gives you a feeling of accomplishment. And that brings happiness. And as writers, we know that can be in short supply some days. Write On!