g1smd - 11:52 pm on Nov 17, 2012 (gmt 0)

It's hard to say "how long" as very often the new redirected-to URL is also added to the site navigation at the same time as the redirect is added. When the new URL is crawled, it's hard to say whether Google got the clue from the site navigation or the redirect. I just know that many of the new URLs can be crawled within 24 to 72 hours of the change.