A small windows service to limit the master volume to XYZ percent. The maximum allowed percentage is time controlled.
If not already present, create the directory C:\ProgramData\SoftwareLimiter. You need to place a config.txt in this directory. For a start, you could use the one
from this project.
The file format is very simple; each line contains a time followed by a space followed by the maximum allowed volume. For example, to limit all sound between 22:00 and 8:00 to 35%:
00:00 35.0
08:00 100.0
22:00 35.0
And that's it.
Should work with all recent windows versions (no, Windows XP is not recent).
You need .NET Framework 4.5.2. Then use installutil.exe as discribed in this stackoverflow thread.
As long as your users do not have admin rights, they won't be able to circumvent this.
3-Clause BSD. Basically: do whatever you want.