Push notification can take up to 10hrs to arrive especially for incoming transactions. I mainly use the notification to know when their is incoming transactions because the transaction does not appear even when you open and refresh the app. When I get a notification I go to "coin control" to verify the amount.
I learnt that it's cause of traffic in the groundcontrol-bluewallet.herokuapp.com server that's causing the delay in notification.
I suggest we should have multiple servers or alternatives for app notifications.