Just installed this. Seems to be very intuitive to set up and use (usergroup permissions need to be set; off by default). I have it set for Administrators use only and have created a test post set for posting tomorrow morning (about 5 hous from now). I logged in as a regular member and could not see the test post - so far so good. :)
I really like this addon. I've seen a couple of similar ones over the years, but this is the first that I've found to be very simple to use. You create your threads/posts as normal, and then right below the usual "Attach files" and "Preview" options you'll see a "Post date" option with a drop-down menu that allows you to set the date and time. After that, you click the "Post thread" button as normal. Only you will then be able to see the thread/post in whatever node/thread you're posting in, so that you can go back and easily edit it whenever, but no one else will see it until the scheduled post time.