what does this code means?

hello,

i have a page called cronjob with next code:

add_action('plugins_loaded', 'wp_cron_init');

///////////////////////
function wp_cron_init() {
	// first, get the current time
	$wp_cron_now = time();

	$this_year = date('Y', $wp_cron_now);
	$this_month = date('m', $wp_cron_now);
	$this_day = date('d', $wp_cron_now);
	$this_hour = date('h', $wp_cron_now);
	$daily = mktime(0, 0, 1, $this_month, $this_day, $this_year);
	$hourly = mktime($this_hour, 0, 0, $this_month, $this_day, $this_year);

	// fetch the timestamps
	if ( (FALSE === get_option('wp_cron_15_lastrun')) 
		|| (FALSE === get_option('wp_cron_hourly_lastrun'))
		|| (FALSE === get_option('wp_cron_daily_lastrun')) )
	{
		update_option('wp_cron_15_lastrun', $wp_cron_now);
		update_option('wp_cron_hourly_lastrun', $hourly);
		update_option('wp_cron_daily_lastrun', $daily);
	}
	$wp_cron_15_lastrun = intval(get_option('wp_cron_15_lastrun'));
	$wp_cron_hourly_lastrun = intval(get_option('wp_cron_hourly_lastrun'));
	$wp_cron_daily_lastrun = intval(get_option('wp_cron_daily_lastrun'));

	if ($wp_cron_now > ($wp_cron_daily_lastrun + 86400)) {
		update_option('wp_cron_daily_lastrun', $daily);
		add_action('shutdown', 'wp_cron_daily_exec');
	}
	if ($wp_cron_now > ($wp_cron_hourly_lastrun + 3600)) {
		update_option('wp_cron_hourly_lastrun', $hourly);
		add_action('shutdown', 'wp_cron_hourly_exec');
	}
	if ($wp_cron_now > ($wp_cron_15_lastrun + 900)) {
		update_option('wp_cron_15_lastrun', $wp_cron_now);
		add_action('shutdown', 'wp_cron_15_exec');
	}
}

//////////////////////////
// these execute the various hooks
function wp_cron_15_exec() {
	do_action('wp_cron_15');
}

function wp_cron_hourly_exec() {
	do_action('wp_cron_hourly');
}

function wp_cron_daily_exec() {
	do_action('wp_cron_daily');
}

?>

PHP:

what i want to know, how long does it ake to activate the cronjob acoording this code? is it set to every 3600 sec? i want to ste it to 12 hours, but i dont understand it

thnx,

 

You probably subscribe to an action like : add_action('wp_cron_hourly', 'your_function_here');

Then in your function access an option like get_option('my_plugin_last_run') which you would also set after you run your function.

add_action('wp_cron_hourly', 'my_plugin_cron_12h');

function my_plugin_cron_12h () {

  if (time() > get_option('my_plugin_last_run') + (60*60*12) ) 
  {
    // do your thing.

    update_option('my_plugin_last_run', time());
  }
}

PHP: