I can't get Twitter or Instagram to show up for me. After waiting an hour I opened the apps and both had updates. I never received a sound or notification. I've tried with the apps closed as well as open and in the app switcher.
Everything seems set up in the Notifications setting. I have them turned on and set to show on the lock screen. Email, texts and phone calls have worked well with Notification Center. Maybe I'm not understanding how this is mean't to work with the other two apps.