How much time does it take for an area to develop its own distinct accent?

Answer 1

Good question! There's actually no clear answer for this; it depends on a lot of factors, including how we define "distinct." Some factors that can speed up or slow down accent change include (but are by no means limited to): contact with other accents or languages, social incentives to sound different or similar to certain groups of speakers, policies about language use, and simple chance!

If you're interested in learning more about this, search for information on sociolinguistics (especially language variation and change); there's a lot of great stuff out there!