wp_schedule_event triggers three times

Hi there,

I have created a wp-cron event the recreate my bbpress sitemap. Y scheduled daily but, dont know why, it is being fired three times, here is my code that I put into functions.php in my theme:

function generate_sitemap () {

	$url = get_bloginfo('template_directory') . '/generate_sitemap_forum.php';

	read_url($url);

	$body = '<p>Sitemap regenerated at '. date("j \d\e F \d\e Y, H:i:s e O") . '</p>';

	send_email(' ... ');

}
add_action('generate_sitemap_hook', 'generate_sitemap');

if (!wp_next_scheduled('generate_sitemap_hook')) wp_schedule_event(time() + 64800, 'daily', 'generate_sitemap_hook');

“read_url” execute the url via curl, the execution time is around 2 mins. Im having this issue with another plugin too.