Then, rather than setting the "check at" interval to something fixed (which also works well), you can have the app check in the background what it should do.

So you can do things like: performSelector:withObject:afterDelay with a custom message after a custom number of starts, or a minimum number of starts after the app has been used for such-and-such a long time.

At the same time, you can monitor the reviews (frequency & stars) and vary over your stats over time. Unfortunately you can't straight A/B test at the same time, as you don't know who wrote which review, but you can A/B test if you separate them by time.

Hope that helps. Feel free to contact me directly: einar@lcrnd.com