Windows has it integrated
Create a shortcut anywhere on the computer,wherever it is easiest for you. When it asks for the file during the begining of the wizard enter
shutdown.exe -s -t 0
^^That is a one step shutdown. Without it,the shortcut would only bring up the shutdown prompt,where you then must click shutdown,restart,or log off.
Go to Accesories>>System Tools>>Scheduled Tasks.
Click add new task.
Browse for the shortcut you just created. Select and time and how often you want the action to occur(For you,every night at 12).
Then finalize. You now have auto shutdown.