By default reminders queue is set to be checked every 5 minutes, but it can only be checked when someone visits the site, so for example if you don’t have users visiting your site for 30 minutes – then six of your 5 minute checks won’t run.

To setup a cron job you need to create an hourly cron job that will trigger this url on your site: YOURSITE.COM/wp-admin/admin-post.php?action=latepoint_route_call&route_name=reminders__process_reminders

You can use any of the free cron services available online, one of them is