Cron automated tasks

The term 'Cron' refers to the automated tasks that your site runs periodically. It takes care of, for example, checking whether or not updates are available for Drupal core, and for your contributed modules, and themes.

By default 'Cron' runs every three hours, which can be changed to every hour, every 6-hours (or more). You can run cron anytime you like from the top of the "Reports" > "Status report" page. Contributed modules are available for additional cron functions.

Or use your server's Cpanel (or similar). You can run it on certain minutes, hours or days, or within a range, like  weekends or night midnight to 5 in the morning, see related for cron's flexibility and usefulness. 

Use case, send a hundred emails every ten minutes from midnight to three in the morning every weekday but then more during your busy season like around holidays.