I should put this in documentation, I’ll go do that now.

On the Edit page for the post:

1. In the options box, make sure “publish” is NOT checked (nothing else should be checked, but that is the default).

2. Press Submit to save the post.

3. To retrieve the post, click the “Content” link in the sidebar. A page listing all your content will appear, including this draft post. In the status column, your post will be “Not published.”

4. When you want the post to be published, check “publish” and press Submit.