Edit crontab:

sudo crontab -e

The first time you might have to choose your preferred editor (like vim).

0 4 * * * /sbin/shutdown -r +5

It would reboot your system every day at 4:05am. (4:00am + 5 minutes).

Finally, restart crontab service:

sudo systemctl restart cron

Reference:
https://askubuntu.com/questions/13730/how-can-i-schedule-a-nightly-reboot