“Advanced Classifieds and Directory Pro” uses the CRON system of WordPress for some automated tasks like,
- Notify users about their expiring listings
- Move listings to expired state
- Notify users about their expired listings
- Remind users to renew their listings
- Delete expired listings those reached the deletion threshold
The CRON system of WordPress is not a real Unix CRON due to the PHP way to work and relies on site traffic to work. A site without traffic will have the CRON system not working.
But, it’s possible to trigger the CRON system externally, using the service many providers make available on their control panel or using an external periodic call to a special WordPress file, wp-cron.php.
There are many external services; with different pricing schemes (some are free) which let one to configure such periodic call.
One of those services is EasyCron. https://www.easycron.com/cron-job-tutorials/how-to-set-up-cron-job-for-wordpress