How can I forcibly shut down my Mac at an appointed time?
Ok, so further to my previous answer, I can walk you through getting cron (a built in UNIX schedule service) to run a scheduled shutdown command for you.

It will run as root and will be forced.


Open Terminal (/Applications/Utilities/Terminal)
Input sudo crontab -e


You'll need to enter your login password and then press enter.

You'll now be in a text editor (vim). Carefully input the following keystrokes.


Press i once (this will allow you to enter text)


Let's say you want the machine to shutdown at 2am every day, we'd now enter:

* 2 * * * /sbin/shutdown -h now


If you wanted the machine to shutdown at 2:30am every day, you'd enter:

30 2 * * * /sbin/shutdown -h now



When you've typed this in, press esc
Then press shift+z shift+z (that's uppercase "z" twice, to writes the changes and quit the editor)


You should now be dropped back to the command line where you started.

You're done!