Fletcher Penney created the original entriescache Blosxom plugin. It is designed to cache all the articles and their creation dates in a Blosxom blog to avoid the overhead of scanning the file system for new/modified files. He merged the meta plugin functionality into the plugin to allow authors to date their entries without relying on the file creation date (this makes it easy to move from one web hosting provider to another without having your article dates get reset).
Unfortunately, articles posted to a Blosxom blog with meta-creation_date's in the future would be displayed immediately. I had wanted to modify Blosxom to allow me post articles with future creation dates and have them hidden until that date. After a request for this functionality on the Blosxom email list, I looked into the required modifications and found it wasn't too difficult to make them.
You can download the modified plugin here. Let me know if you have any questions or comments.