iOS background fetch, where and when to schedule

Question

I want to use background updates for one of my apps, and little bit confused about the logic of background fetch - where and when I have to call setMinimumBackgroundFetchInterval: method? Tutorials on the web are advising to call it on application: didFinishLaunchingWithOptions:, but what happens when application is launched manually by user before the scheduled background fetch is not yet started? Does it get cancelled and re-scheduled, or one more fetch operation is scheduled for the app? Please, advise! Thanks in advance for the comments and answers!