scheduling a task to test wp-cron

gistfile1.txt

if (!wp_next_scheduled('my_task_hook')) {
  wp_schedule_event( time(), 'hourly', 'my_task_hook' );
}

add_action( 'my_task_hook', 'my_task_function' ); 

function my_task_function() {
	wp_mail('you@yoursite.com', 'Automatic email', 'Hello, this is an automatically scheduled email from WordPress.');
}

And to delete the item
    delete_action( 'my_task_hook', 'my_task_deactivate' );
    // clean the scheduler
    function my_task_deactivate() {
    wp_clear_scheduled_hook( 'my_task_hook' );
    }

But not always are 3 time values enough. Luckily you can expand the control via a filter.

    add_filter( 'cron_schedules', 'filter_cron_schedules' );
    // add custom time to cron
    function filter_cron_schedules( $param ) {
    return array( 'once_half_hour' => array(
    'interval' => 1800, // seconds
    'display' => __( 'Once Half an Hour' )
    ) );
    }