cron_schedules not working

Hello,

I am trying to add custom intervals for the WP cron.
Here is the code:

add_filter( 'cron_schedules', array('invit0r', 'filter_cron_schedules')  );
...
function filter_cron_schedules($schedules) {

		$schedules['every_minute'] = array(
			'interval' => 60,
			'display' => __( 'Once per minute' )
		);

		$schedules['every_five_minutes'] = array(
			'interval' => 300,
			'display' => __( 'Once five minutes' )
		);

		$schedules['every_ten_minutes'] = array(
			'interval' => 600,
			'display' => __( 'Once ten minutes' )
		);

		$schedules['every_fifteen_minutes'] = array(
			'interval' => 900,
			'display' => __( 'Once fifteen minutes' )
		);

		$schedules['every_half_an_hour'] = array(
			'interval' => 1800,
			'display' => __( 'Once half an hour' )
		);

		return $schedules;
	}

Yes, I am calling add_filter in a class called invit0r (it will be a plugin).

add_filter fires the function, but it doesn’t add the intervals. Does it have some kind of limit, not allowing intervals below one hour, or I am writing something incorrectly?