I've read this question and the answers links through to Jenkins. Looked into it but was way over my head to install and set up. The other answer links to this page which talks about running cron tasks with drush commands. What I want obviously is the opposite.
With the endgoal in mind of just doing backups and updates, it seemed pretty straightforward the I could create a crontab that triggers a php or sh script with drush commands in it. The only thing I can't seem to find is a way to construct such a script.
I did google this, but I keep getting information to do the opposite thing being trigger cron with drush.