It is easy to script, as ebook-convert (cli interface to Conversion) accepts *.recipe files, and will endeavor to match it to the builtin recipe file if needed. However, that won't add it to the library, you will need to then call `calibredb add`. Then run that script via a scheduled task (cron/systemd/launchd service for *nix users
).
Another option would be to add a scheduled task that opens calibre each day.
Personally, I don't use Fetch News, but I do keep calibre open.