I just want to correct a factual error in your post. I've noticed that the review process time used in a variety of responses continues to creep upwards -- here, it's up to three weeks.
As it currently stands, as per Apple's published status, 95% of applications are approved within 8 days.
After Apple publishes a new version of your app, your users must notice the update and choose download it--my guesstimation includes that. If you'd prefer to use 8 days, that is still a lot longer than the next HTTP request, which is how long it takes users to get a new version of a web app.
As it currently stands, as per Apple's published status, 95% of applications are approved within 8 days.