It used to be called Quiet Hours, but now it's Focus Assist.  The name means that you won't be interrupted during a game, presentation or late at night. So you can stay 'focused'.  Get It?

Well, what it does mean is that you can finally set the hours at night that you don't want to be disturbed. Same with gaming. No longer do you have to toggle it on. With the right settings, anytime you're playing a DirectX game, the system will turn off notifications.