You can push a scheduled task through Group Policy on a computer level. The task you want to push should be a batch file with the code something like the example below.
The above will just force shutdown the system.
The above will force restart the computer.
To create a batch file type the above code into notepad and save the file with a .bat extension instead of .txt
If you have any other questions let me know. This shoul help you get on the right track. If you are unfamiliar with creating or editing Group Policy objects please read up on this before making changes as some changes are very powerful across a domain.