If an app attempts to send a notification to an iOS device that is either powered off or has no network connectivity push notifications need to be kept in queue.
For how long does Apple retain notifications to allow the device time to contact the APNS servers?
Best Answer
What you are referring to is covered under Quality of Service component of Apple push notifications. It's addressed in the following linked Apple Developer documentation:
and
Referring the Local and Remote Notification Programming Guide should address your concerns related to Apple push notifications.