User blog comment:Quiksilvr/The date-time synchronisation error and what you can do about it/@comment-49.151.122.238-20160628024535/@comment-27945602-20160628083733

There are 2 types of notification. One type is online based notification. apps like messaging app requires developer's server to send notification. It sends token with message to Apple's server and relays it to coreasponding device. This is the reason why you can't get notifications on offline. You need Internet connection. The other types is like timer. On certain time the app itself sends notification via API with the message. The exact time should be pre loaded with the message. When the times comes, you get notification even if you are on offline. Real Racing 3 uses both types of notification. They use offline way in the case of car repairing. Even if you click notification on offline your cars are not repaired. They just set timer and notify the time to make you go online. Or if your WTTT ranks goes down, their server sends message (online) to you. You only get this when you're online

For more information go iOS developer documents.