Schedule apt-get script using cron

It's a better idea to use "unattended-upgrades" instead.

Its purpose is to keep the computer current with the latest security (and other) updates automatically. [1]

To install:

sudo apt install unattended-upgrades

Read more about how to get it work: here.

To address your question, you can edit /etc/crontab file and run your commands using root user without the need of using sudo in your own "crontab" file.

nano /etc/crontab

and add a line like:

45 21 * * * root apt-get update > /home/ravexina/out.log

which runs apt-get update using root user at "21:45" every night and logs the output to /home/ravexina/out.log.