Any of these would work fine for your idea and not be very difficult to do. (Assuming the site doesn't have any anti-bot measures). You'll need to create a cron

Any of these would work fine for your idea and not be very difficult to do. (Assuming the site doesn't have any anti-bot measures). You'll need to create a cron that runs the automation script or opens a browser with your greasemonkey script installed. Sometimes you can even do these with pure curl. POST the login form, get back the necessary cookie or token, then request the download URL, if it's easily predictable.