Normally push notifications do arrive quite quickly. But there are some rare cases where we’ve seen them get delayed:
Delays for notifications on Android Devices:
- Some home and commercial wifi routers will cause the device’s connection to Google’s FCM/GCM servers to be closed. The device later re-opens the connection and receives the delayed notifications. (Discussed here: https://groups.google.com/forum/#!topic/android-gcm/Y33c9ib54jY)
- Some Android devices can enter a low power mode when their battery is low that may cause slight delays in receiving notifications.
Delays for notifications on iOS devices:
- As with Android, some wifi routers will cause iOS notification delivery delays.
- Notifications may be delayed if “Restrict background data” is checked for the app, if Wifi-Optimization is turned on in the advanced settings, or if priority mode is enabled.