Research is a lifelong occupation so it's hard to factor it in, but I reckon most books take 5 months from start to finish.
There is no greater impediment to progress in the sciences than the desire to see it take place too quickly.
What happened in the interim is, billions of records have been digitized. Historians and scholars have always used genealogical records to tell the story of American history. It takes months and years of research. I can't even tell you how laborious that is. You have to be somebody who has a lot of free time, like a professor who can take tenure or someone with a great deal of leisure.
It takes me three or four years to research and write each book and the individual stories stay with you for a long time afterwards.
The minimum I need is six months to allow for dithering, procrastination and the research. The research times varies from book to book; some are faster because they're based off resources I have at my disposal.
I jealously guard my research time and I love fully immersing myself in those dusty old books and papers. It's one of the most enjoyable parts of my job.
I work on one book at a time. And yes, I am immersed. Six days a week for four to six hours a day. In between books, I stop writing for as much as two to three months, but during that time, I do research and think, plot and plan the book.
A lot of my research time is spent daydreaming - telling an imaginary admiring audience of laymen how to understand some difficult scientific idea.
You do not give a great biographer a timetable. You let them do their work and, in due course, publish it.
All my books take a long time to research. I spend several months researching before I start writing, and in the middle of writing I often have to stop and look up stuff. At my local library, I am one of the best customers! The research takes several months.
It takes me three months of research and nine months of work to produce a book. When I start writing, I do two pages a day; if I'm gonna do 320, that's 160 days.
It usually takes me about three years to research and write one of my historical sagas; this is one reason why I take medieval mystery breaks, for they can be completed in only a year.
I'm not a foodie; I'm an eatie. I don't have anything against foodies. I just don't have the time or the interest to do that much research.