Consider the following scenario:

• You enable a RSS feature on an Microsoft Office SharePoint document list.
• You set the RSS refresh interval to be less than 120 minutes.
• You add a RSS viewer Web Part on an Office SharePoint page.
• You configure the RSS Feed URL of the Web Part to use the RSS address of the Office SharePoint document list.
• You make sure that the RSS Viewer Web Part works correctly. Then, you change some items in the Office SharePoint document list.

In this scenario, the RSS Viewer Web Part does not display the changes as expected. You have to wait two hours for the RSS Viewer Web Part to display the changes in the Office SharePoint document list.

http://support.microsoft.com/kb/982191