This is an alternative for Cron

Issue the following command in terminal:
/sbin/shutdown -h +300

Command Details:
sudo : This is to execute the command as root, you will need the password here.
/sbin/shutdown : Command to shutdown the computer.
-h : This tell the shutdown command to power off i.e. halt.
+300 : The minutes before scheduled shutdown, here it is 300 minutes.

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