Push notifications are delivered by the Apple Push Notification Service (APNS). This service is run by Apple, not by SCRUFF. When a triggering event occurs in SCRUFF (e.g. new message, new Woof, new unlocked Private Album) we send the notification to Apple for delivery through APNS, and they are responsible for pushing the notification to your device in a timely fashion. As SCRUFF does not control the uptime of APNS, we cannot guarantee that all push notifications will be delivered, or delivered in a timely fashion.
If you are not getting any push notifications, please verify that Notifications are enabled for Scruff. From the iPhone home screen: