Glenn Damato's sailing memoir, Breaking Seas, sold over 20,000 copies in a little over two years. This memoir tells the story about an overweight, middle-aged software instructor who, dissatisfied with his humdrum life, quits his job and embarks on a sailing adventure around the world, a journey for which he is terribly unprepared.
War and Peace wasn't written in a day. In fact, it took Tolstoy six years to write the novel. I'm not sure if anyone knows how many hours he dedicated to writing each day, but I assure you, he prioritized his writing time.
If you have a busy life and have been thinking of writing a book, you're going to need to do the same thing as Tolstoy. It'll be easiest if you embrace this concept: in order to create something of value, you're going to have to give something up. There's no way around that.