As far as I am aware from reading around the subject after reading the millionth "the app store sux" article. The best indication we have is from this article: http://www.marco.org/98546611

  "In all cases, the reviewers don’t touch the app until the
  day before approval or rejection. And they don’t seem to
  interact with the app for more than a few minutes.

  The app just sits there for 6-8 days, untouched, then goes
  through an approval or rejection process that, as far as I
  can tell, takes less than 20 minutes for a complex app (and
  probably much less time for a simple one)."