Set time & date for posting content. Not on posting-page.

Almost anything is possible if you’re willing to custom code a solution ?? Including what you want. The posts that are scheduled for future publishing could be assigned a unique category or tag term. Then alter the postings-page query to exclude posts which have that particular term.

You can use the “pre_get_posts” action to modify post queries. The trick is distinguishing one query from another. If the query you want to alter is for your home page, you can use WP_Query::is_home() to ensure you’re changing the correct query. Determine what the ID is for the term of whose posts you want to exclude. Set it as the “category__not_in” query var. For example:

add_action('pre_get_posts', function( $query ) {
  if ( $query->is_home()) {
    $query->set('category__not_in', [ 1234,]); //use correct term ID here
  }
});

If your theme is not subject to periodic updates, you can add this to its functions.php. But your code will be removed if a theme updates. To protect your code from updates, you could create a very basic plugin to contain all of your custom code. Creating a plugin isn’t as difficult as it might sound.