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I doubt that you can get a definitive answer from a non-googler (and googlers' non-disclosure agreements sometimes make them fairly closed-mouthed), this will depend on how fast the new content is indexed and how soon after that the indexed results get processed by Google's ranking algorithm. To get the fastest results 1) resubmit changed pages for indexing right after they are changed. The only other things you can do is 2) don't limit Googlebot's crawl rate or, if it has been limited, fix that. 3) don't limit (in robots.txt, etc.) what you allow googlebot to crawl. (Who would do that? I did, after watching googlebot crawl some wp folders where I felt it had no business.  Corrected that fairly quickly.) Generally, I see an effect on SERPs fairly quickly - a day or 3. However, if you are in a very competitive market, there's always that brownian motion caused by what your competition does...:)

Thanks and good luck!