If you would like to run the script as Admin/Sudo, then:
sudo crontab -e
and paste the following at the bottom of the file:
59 23 * * * sh ~/Desktop/Script.sh
That will run at 23:59 everyday. The format for cron is:
minute (0-59), hour (0-23, 0 = midnight), day (1-31), month (1-12), weekday (0-6, 0 = Sunday), and a star(*) for all the time.
To run a script without root privileges:
crontab -e
and repeat as above.
Cherio!