The only time Apple gave out hard numbers on their review setup, a couple of years ago, they had two reviewers check each submission, with an average of 6.5 minutes per reviewer per submission spent checking it. Obviously, that average contains quite a bit of variation.
Interesting. I don't think I've ever had one take < 1 hour, and most are 3+ hours from 'In Review' to 'Processing for App Store' or 'Rejected'. 12-24 hours is fairly common for me, and I just had one approved the other day that was 'In Review' for ~48 hours.
