The WordPress integration is working like this:
The Post_To_WordPress feature was called everytime user click on the Publish/Approve button (appear both for scheduled post or direct post).
So, after user push the Publish/Approve button, it will check the WordPress configuration.The WP button will change the color to green if the configuration are correct and the setting is enabled.
If the configuration are correct and the user enabled the settings then it will post to WordPress also.