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.