Windows 8, like Android and iOS, features an apps notifications
function, alerting you when you receive new messages, calendar events
and email. Unfortunately, Microsoft offered users scant options for
silencing those notifications. You could either shut them off for a few
short ours, or turn them off entirely. Thankfully, Microsoft has
rectified this omission, adding a new Quiet Hours function in Windows
8.1 that lets users schedule when notifications should be active and
when they shouldn’t.
search for 'notifications' from start screen select it then select '
notification settings'
When enabled, Quiet Hours ensures your notifications don’t make any
noise or cause the screen to light up when your Windows 8.1 device is in
sleep mode. Your notifications will automatically be restored whenever
you start using your device or Quiet Hours are over.