In Cortana, press the menu button (3 lines top left corner) from the menu go to notebook. In the notebook there should be the option for quiet hours and options for who can break through etc.
Also, just expand the Quick Actions in Notification Center to show all the buttons and Quiet Hours should be there. Just tap it on, tap it off. If you use it a lot (like I do) it should be in your prime row to show when the field is minimized...