What should I expect once my iOS app is approved?

Once your app is approved, it can take up to 24 hours before your app is searchable on the App Store.

Something to note is that sometimes there is a delay for in-app purchasing function through iTunes (subscriptions do not immediately work) due to Apple's processing. We've learned the experiences
 range from 2 to 36 hours for it to be fully functional.

A suggestion is to have a soft launch, making it available a day before you announce it. That would work as a buffer, to let it work through apples servers.

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