It definitely seems like multiple people can be involved if there is uncertainty on whether to reject the app. From experience, I've found that if my app is sitting in "In Review" status for more than a certain number of hours, it's likely to get rejected.

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.

They also check more expensive apps more thoroughly, according to the iOS developer guidelines.

That checks out with my experience. Typically an app will go from 'in review' to 'processing for the app store' in about 15 mins.

My app always takes many hours to review. There are a lot of buttons.

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.