The plugin uses wp_cron subsystem from WordPress for scheduling it’s automatic importing process, which is not a real cron system, but a ‘pseudo-cron’ (false cron). This means that it needs visitors to the website, so it can get fired up and running.
If your website does not have visitors, the wp_cron will not run until the first visitor comes.
To fix this issue, please create a free remote cron job calling the root URL of your website, here: cron-job.org – Free cronjobs – from minutely to once a year – you can set it once per hour.
Like this, you will simulate a website visit each hour, and the wp_cron system will run each time.