Once you submit, KDP's review usually takes up to 72 hours, often less. The book can then take a little longer to appear in every marketplace. Order a proof copy for a paperback before you publish; printing and shipping add days.
Writing time is the real variable
Drafting is where most of the time goes. A clear outline and a story bible cut rewrites.
KDP's rules change from time to time. Check KDP's own help pages for the current requirements before you publish.