How to set up your CRON task for delayed posts ?
You have 2 options:
1) Setup via crontab (for users with technical / Linux knowledge)
IMPORTANT : The CRON’s line you’re going to configure must be executed as a web server request by prefixing your line with lynx application (text browser), or any wget / curl commands that implies to use the web server engine. This allows that your request will be successfully executed in the web server context and get all the PHP environment variables as needed for your PrestaShop execution. DO NOT put the physical path of the script, and only put the script URL that you can find in the module’s back-office.
CRON tasks are usually set up by editing a crontab file and adding a line. For example:
0 11 * * * lynx -dump http://www.myshop.com/modules/facebookpswallposts/cron.php?id_shop=1 > /dev/null
This example will execute the URL every night at 11:00AM (this precise example requires that the text based browser Lynx be installed on the server). This is usually only possible if you have a dedicated server. But you can also ask your web host. Some of them let you do this via a control panel on your hosting account.
Refer to https://help.ubuntu.com/community/CronHowto for a good explanation of schedules.
2) Using a third-party service
You can sign up for a free CRON service online on websites such as https://www.easycron.com. All you'll need to do after signing up is enter the CRON URL indicated in the module.