I'll chip in some misc notes from bios I have read.
Someone (from an intro I have lost) said that Balzac damaged his writing skill by essentially being forced by life to write too fast ... that he lost some sense of subtlety, and once it was gone, a few of his later books and ultimately his health suffered and he died young.
Elsewhere I read in bios that some people's books take years to write as they gestate. Particularly the ones that require both research and a premise that you can't just crank out.
So "in a month" might have caveats.