You should create a script using the directions given by Kees Cook...
You can just copy and paste the information below in any text editor and create the zz-reboot file in the directory suggested.
After that just remember to right click on the file and assign it execution permission.
If you feel like doing in using terminal just:
sudo chmod +x /etc/cron.daily/zz-reboot
To understand better what you're doing remember that in etc folder you generally find configuration files and there you can find cron.hourly, cron.daily and other cron folders.
Cron takes care of executing applications and script at a certain time.
If you want to be strict about the reboot time just digit
sudo crontab -e
so you can edit the croontab for the root user.
If you feel better doing it graphically you can install from the Software Center gnome-schedule.
If you want to modify the gnome-schedule for root user ensure that you run it from terminal:
Have fun playing aroud! :)
great point sBlatt! I was wondering if there's any way to force cron.daily execution time manually