Dylan
Article not ready yet as I hve not tested so I am loath to give you something that may not work. 
You could ask your hosting service what you should do, also there are some Joomla! extensions that will do a Cron for you

The url you need is  found by copying link in the 'Check Download area now' is something like the following "<your site>/administrator/components/com_jdownloads/helpers/scan.php?key=o0ut47eIWH5QD44N8QLwyRmRE" where the key part is unique to a site.

Colin

Thanks for the various explanations of each person, it was very helpful to read.

Hi
For reference the article on CRON jobs ishttps://www.jdownloads.net/documentation-for-v3-9/faq-v3-9/automatic-publication-at-scheduled-times-cron-jobColin