iman Pro local notifications are queued every time you activate the app. At one time, 64 notifications are being queued. This is the maximum notification queue that is allowed by Apple. Ref: here
Each Azan time is counted as 1 notification. In a day there is a minimum of 5 Azan notifications(subject to your configurations). Setting up pre-Azan notifications will occupy more notifications queue for that day. Assuming 5 Azans a day, 64 notifications can last up to approximately 13 days.
Once all 64 notifications have been triggered, you may not get any more new Azan notifications unless you activate/open the app again to refresh the local notifications queue.
iman Pro users who allowed location permissions with "Always" will enjoy automatic notifications queue refresh. This is because iman Pro is now able to run in the background every time there is a significant change of location detected.
In other words, iman Pro users with this configuration do not have the need to open/activate iman Pro app at all and enjoy continuous Azan notifications as long as he or she travels around once in a while.