Actually, you could just use the builtin task scheduler in windows.
(programs\accessories\system tools\scheduled tasks)
also (control panel\scheduled tasks)
It requires the task scheduler service to be active. (I think it is by default, mine is disabled though as I dont use it).
There is a command, usually at c:\windows\system32\shutdown.exe
Which can be called with the -s parameter to shutdown. So if you schedule that as a task, you can set it to shutdown your computer everyday at a specific time or similar.
Not sure whether the task scheduler accepts parameters to programs, otherwise you could create a shutdown.bat file with:
Then, schedule that instead.