There is no ability to schedule 'do not disturb' quiet times.

Use case 1:
User goes into a meeting, sets 'do not disturb': silence mode, for 2 hours.
All audio and system sounds are off for 2 hours and come on again thereafter.

Use case 2:
User sets an auto quiet time schedule so that on weekday evenings all audio and system sounds and vibrations are turned off at 23h and turned back on again at 08h. This way neither the user nor their roomsharers are awoken. User doesn't have to remember to turn it on again and miss important notifications in the morning.

Use case 3:
User wants to play 

This is expected in all desktop and mobile operating systems.
It is present in Android, iOS, OSX, Windows, but not Gnome or KDE.

There should be a button in the volume applet (or another applet), which can:

a) set the mode (indefinitely), 
b) set the mode for a fixed period (i.e. in hours and minutes)
c) provides an option to set up a schedule.

The modes should be: 
a) silence, 
b) vibration only (for those devices which can), 
c) low, 
d) normal.

The schedule should allow daily times for a week.