Hi,
First, you need to configure your HikaShop cron task:
www.hikashop.com/support/documentation/5...ashop-cron-task.html
You can use the normal cron task of HikaShop we provide and have it run every 15 minutes.
Make sure the cron task is working as per the instructions on that page.
Then, in both the reminder plugin and the waitlist plugin settings (via the joomla plugins manager), you can find a setting "Period" (or "frequency") and a setting "Last update".
In the first one, you need to enter 43200, which is the number of seconds in 12 hours.
And in the Last update, you need to enter the next time you want the plugins to run with the unix timestamp format.
You can use that tool to get the number to enter there:
www.epochconverter.com/
Also, make sure the plugins are enabled with an access set to "public".
That way, they will run once the next time you configured + the period. And then, they will run every 12 hours.
So for example if now is 10AM and you configure the "last update" to be 3PM, the next time the plugins will be triggered will be the next day at 3am, and then the next day at 3PM, etc.