End-to-End Cron setup.

Hi,

I am looking for a short guide on End-to-End Cron setup, with following steps I already did and some still waiting.

Purpose : I have some big SQL which I cached using set_transient with timeout, however I want to run this SQL and use set_transient in cron so my end user never experience the slowless.

Steps I thought so far,

1. Disable the Cron job for every page load.
A: define(‘DISABLE_WP_CRON’, true) in wp-config.php file. (DONE)

2. Run cron at regular interval from your system.
A: Setup cron entry with “wget -q -o – -O – -t 1 http://example.com/wp-cron.php > /dev/null 2>&1. This sets output and log goes to null, quite mode and retry once only. (DONE)

3. setup the cron schedule for every 20 mins.
A : to add this filter
add_filter( ‘cron_schedules’, ‘cron_add_20mins’ );
function cron_add_20mins( $schedules ) {
// Adds every 20mis to the existing schedules.
$schedules[‘every20mins’] = array(
‘interval’ => 1200,
‘display’ => __( ‘Once Every20mins’ )
);
return $schedules;
}
(BUT I don’t know where to add this, so it execute only one time).

4: Schedule an Once Every20mins job.
A: to add this two filters.
function my_activation() {
if ( !wp_next_scheduled( ‘my_hourly_event’ ) ) {
wp_schedule_event( time(), ‘hourly’, ‘my_hourly_event’);
}
}
function do_this_20mins() {
//check and cache all SQL object with set_transient.
}
add_action(‘wp’, ‘my_activation’);
add_action(‘my_hourly_event’, ‘do_this_20mins’);

TWO QUESTIONS :
1. I guess action ‘my_hourly_event’ is not right if I want to make it every 20mins, so what it could be ?
2. I don’t know where to add this, so it execute only one time.