Create a custom cron interval

Custom CRON interval

/* ----------------------------------------
* ADD CRON CUSTOM INTERVALS
----------------------------------------- */

add_filter('cron_schedules', 'xxx_cron_every_two_days');

// add a cron interval every 2 days
function xxx_cron_every_two_days( $schedules ) {
	$schedules['every_two_days'] = array(
		'interval' => 172800, // in seconds
		'display'  => __('Every two days', 'xxx')
	);
	return $schedules;
}