After jumping through hoops trying the slick but expensive 'premium' schedule plugins with similar (but way more restrictive) function, I found this little gem. This is the simplest, most intuitive and seemingly most robust one of the lot.
You view a visual Calendar in Posts, hover on a day and add new post. If you have existing scheduled posts, they are visible - and you can even drag and drop them onto a new date. You can also see Draft posts and drag them into the calendar!
A small caveat might be that creating a new post in the calendar shows only a title and content field - and has no category option. I think it uses the default WP one (i.e.: Uncategorised, or whatever you've renamed it to). However, because you can either quick edit or full edit directly from the calendar once you've created the new post, you have the usual WP post window and set category, add media and post format etc.
Because the plugin has no settings (and needs none!) and needs no setting up, the above is an extremely moot point.
This plugin is a gentle bit of genius. Hats off to the developers/designers - this is singly the best new WP plugin I have tried in ages.
(Although I don't want to laud it too much in case they start charging a fee for it! ;-)