In a normal-use scenario, where the incoming load is consistent and even, Azure Notification Hubs can process at least 1 million push notification sends a minute. This rate might vary depending on the number of tags, the nature of the incoming sends, and other external factors.
During the estimated delivery time, the service calculates the targets per platform and routes messages to the Push Notification Service (PNS) based on the registered tags or tag expressions. It is the responsibility of the PNS to send notifications to the device.
The PNS does not guarantee any SLA for delivering notifications. However, most push notifications are delivered to target devices within a few minutes (typically within 10 minutes) from the time they are sent to Notification Hubs. A few notifications might take more time.
Note
Azure Notification Hubs has a policy in place to drop any push notifications that aren't delivered to the PNS within 30 minutes. This delay can happen for a number of reasons, but most commonly because the PNS is throttling your application.