Use restrict_manage_posts to unset default filter?

Hi, I’m trying to change the filters available on the edit posts listing in the admin screens. I’ve gotten most of what I want to get done done, but I need to remove the “Show all dates” filter and replace it with my own. I’ve figured out how to add a new one using restrict_manage_posts, but I’m unclear on how to remove the default.

Here’s what I’ve tried, but it appears that $defaults does not receive any values:

add_action('restrict_manage_posts','my_restrict_manage_posts');
function my_restrict_manage_posts($defaults) {
	unset($defaults['m']);
	return $defaults;
}

I got the $defaults[‘m’] bit from the name of the selector, but obviously this is wrong.

Any pointers? I feel like I’m close, but just can’t get there.