That’s odd because that works fine for me on inphotos.org where I occasionally use scheduled posts. Can you debug the plugin, look for the function “wp_cache_post_edit” and perhaps add an error_log() or mail() in there to alert you when it’s kicked off. It should fire whenever the post is published.

It might also be the case that you’re not getting sufficient dynamic traffic. The post is published by the WP Cron system and that needs visitors who request pages that aren’t cached. I know it’s unlikely, but if every single page on your site is cached then there’s a chance no PHP will execute.