Using get_post_type with a custom URL format?

If you’re doing something in the wp_insert_comment hook, then you should use the 2nd argument, $comment_object, if you want to know anything about the post the comment was for. $comment_object is a WP_Comment object that has a $comment_post_ID property that has the ID of the post the comments is for. You can use that to determine its post type. The URL structure is completely irrelevant.

function wpse_304105_update_time( $comment_id, $comment_object ) {
    $post_id = $comment_object->comment_post_ID;

    if ( get_post_type( $post_id ) === 'top-news' ) {
        // Update post time.
    }
}
add_action( 'wp_insert_comment', 'wpse_304105_update_time', 99, 2 );