Sound Auto

(Android 4.1 or above)
Distribute an app that I made to myself. Forgetting sometimes to mute the mobile phone. App runs in the background. Mutes the audio on the cell phone at 21:30 and turns on at 6:00. You can not change the settings in any way.

How to use it:
When you launch the app there is no screen but you can see the app running in the background if you go to settings> apps> running.