How to Create a Custom Plugin Permalink

I think this answer could help you. Make a custom page template within your plugin and then create a page with that template called Blackout, and redirect users in the plugin to that page.

Help from: Create custom page templates with plugins?

Edit with code sample:

Say you have a page called Blackout, the slug is blackout.

add_filter( 'page_template', 'your_custom_page_template' );
function your_custom_page_template( $page_template ) {

    if ( is_page( 'blackout' ) ) {
        $page_template = plugin_dir_path( __FILE__ ) . 'your-custom-page-template.php';
    }

    return $page_template;
}

As long as you can get the redirect to work properly when it should, this code above should work in conjunction with it to display the page template whenever that page is visited. Now you can customize your-custom-page-template.php or whatever you name it from within your plugins folder instead of the theme.

Edit, I got this working:

function blackout_redirect(){
    $page = get_page_by_path( 'blackout' );

    if( isset( $page ) && !is_null( $page ) ) {
        if( !is_page( 'blackout' ) && !is_admin() /* && $check_date stuff */ ) {
            wp_redirect( get_permalink( $page->ID ), 302 ); exit;   
        }
    }
}
add_action( 'wp', 'blackout_redirect' );

function blackout_template() {

    if( is_page( 'blackout' ) ) {
        include plugin_dir_path( __FILE__ ) . 'blackout.php'; exit;
    }

}
add_filter( 'template_redirect', 'blackout_template' );

On the Twenty Eleven theme, only a couple other plugins active.