If you update to Joomla 3.8.10, please make sure that you either do a full GitHub update of Fabrik, or disable caching for your lists (in the Advanced settings) or turn off Joomla's System Cache setting. A change in Joomla's cache code in 3.8.10 required a fix in Fabrik, which will be rolled in to the next release, but is currently only available in GitHub.
Scheduled task system plugin
The scheduled task system plug-in has no parameters that need to be set except to ensure that it is published.
This plug-in is required to be installed and published if you want to use Fabrik's Scheduled Tasks features.
If enabled, when a user accesses a page on the site (not an administrator page), the plug-in checks all of Fabrik's published scheduled tasks. If any task needs to be run Fabrik will run that task.
While a task is running, its published state is set to 2 (running) and when successfully completed its published state is returned to 1.
This means that multiple occurances of a scheduled task will not run at the same time. However, if the task produces an error it may not be reset to 1, effectively meaning that the scheduled task will no longer run.
You can see these tasks by filtering the list on 'archived' or 'all'. They will appear with their status column showing an alert icon.
If you need accurate scheduled tasks, which are not dependant on a user hitting the home page, then you should set up a cron job on your server or use a webservice such as https://www.setcronjob.com to trigger a front end page load.