CRON: add a new task

Set a timing interval

add_filter( 'cron_schedules', 'dev__set_interval' );
function dev__set_interval( $schedules ) {
	$schedules['dev__interval__5_minutes'] = array(
		'interval'	=> 60 * 5,
		'display'	=> 'Every 5 Minutes'
	);
	return $schedules;
}

Check if the CRON task already exists

if ( ! wp_next_scheduled( 'dev__a_cron_thing' ) ) {
    wp_schedule_event( time(), 'dev__interval__5_minutes', 'dev__a_cron_thing' );
}

Add action to that new hook

add_action( 'dev__a_cron_thing', 'dev__a_cron_thing__fallback' );

function dev__a_cron_thing__fallback() {

...

}