I tackled it a bit differently so that I could get a good night's sleep.
I installed MacroDroid and use the "Date/Time" trigger. I set it to recognize that 2200 hours has passed and then the Action feature opens Set Volume and then the constraints is set to reduce Notification and System volumes to Zero.
Then I set up another macro to sense the
screen being unlocked and used the
Set Awake Action option to reset all of the volume levels to where I want them during the daylight hours.
It works a treat, I have to tell you. I never get any noises out of my phone at night now. Not even a "Battery Fully Charged" sound.... it is so nice to be able to sleep all night w/o idiots and scammers-telemarketers waking me up.
* MacroDroid - Device Automation - Android Apps on Google Play