Not without some tinkering. If Calibre isn't running, you need to rely on your OS's job scheduler to call the download. There are multiple threads explaining how to do this, the command you need is
Code:
ebook-convert recipename.recipe outputfile
(Don't forget the extension of the output file, it tells Calibre the format.) Then you could use calibredb to add the resulting file to the database, if you wish to.