How often is the RSS feed for WordPress Plugins Directories updated?

Since WordPress has issues delivering email notifications when Users post in the Support Forums for Plugins I’m trying to use an RSS feed instead. The problem is that it doesn’t appear to be updating even though I see users posting in the forums.

Does anyone know how often the RSS feeds for WordPress Plugin Support Forums are updated?

Ex: http://wordpress.org/support/rss/plugin/project-manager-by-tpc