Crony Cronjob Manager
A Plugin for corn job
A good link is to setup corn job is
What does wp_cron() do?
As you receive visitors on your site, WordPress checks your database to see if anything is scheduled to run. If you have a wp_cron() job scheduled every 12 hours, then the very first visitor 12+ hours from the last scheduled run of that function will trigger the function to run in the background. The Cronjob (or Cron Job) sends a request to run cron through HTTP request that doesn’t halt page loading for the visitor.