Thought this was interesting so had a quick search and here is what I found

For linux there are a few solutions depending on the install:

    */5 * * * * pactl set-sink-volume @DEFAULT_SINK@ -2%

or with amixer

    */5 * * * * amixer -D pulse sset Master 2%-

Terminal command to set audio volume? - https://askubuntu.com/a/97945

For windows you can use powershell to trigger the Volume Down Button

    $obj = new-object -com wscript.shell
    $obj.SendKeys([char]174)

Simply add the script to a Task scheduler task (create as a daily task then go into advanced and trigger every x minutes)

Change audio level from powershell - https://stackoverflow.com/a/21362870 Run a task every x-minutes - https://stackoverflow.com/a/4250516