Are you talking about where you put user executable scripts?
/usr/local/bin
I'd just create a script that calls shutdown -h 22:00, make it executable, drop it into /usr/local/bin, then call it from Zorin menu > System Tools > Startup Applications.
As soon as the machine boots, it's got the command to shutdown at the specified time.
Or you can set it to run as a service, so the user never even sees any command prompt. Here's a quick how-to, used to remap the hard drive light to a keyboard light, but you can do the same for the shutdown command:
So let's say you want to name your script "autosd".
Create a text file with your shutdown script in it. Save it to /etc/init.d/autosd.
Set the file as executable:
sudo chmod +x /etc/init.d/autosd
Create a sym-link in the proper run level directory:
sudo ln -s /etc/init.d/autosd /etc/rc5.d/S01autosd
You want to use /etc/rc5.d, the 5th run-level, as that's the desktop... so as soon as the machine boots far enough to get to the graphical desktop, it'll have a command to shut down at the specified time.
You might want to put a wall message so anyone still using the machines don't freak out when it shuts down on them.
More info:
man shutdown
man wall