This article will show you how to add a line code that will make your WordPress feed update every thirty minutes or less if you prefer: Feed the feed 
I decided I would use the WordPress feed widget to put a list of the latest blogs on the right hand side. So I simply dragged and dropped the widget into the sidebar area, like we do with all the widgets and stuff located in the widget section. This way, when anyone loaded any page the latest posts would be listed, genius! I thought and smiled at how easy it was and now people could easily see the latest blogs.
I added another blog and noticed the widget didn’t post the new feed. I clicked the feed button and the feed page appeared with the new blog post, so I went back to the site and refreshed and still the WordPress widget wasn’t showing the new post. hmm 
I searched the web and found some links that said the widget updates every hour. “Okay” I thought, I would wait. So after an hour passed, I checked, and still no updates on the widget feed. grr.. I decided I would search for a fix on the web and nothing really worked. Then I read where the widget takes 12 hours to reload the feed 
That was not happy, so I started searching for more ways to fix this and finally I discovered the answer:
In your wp-admin go to your Appearance then select Editor
Then find your functions.php and add the following code at the end:
// Make the feed update every 30 minutes Feed the feed
add_filter( 'wp_feed_cache_transient_lifetime', create_function('$a', 'return 1800;') );
The blue type of return 1800 means you can change that value to whatever you want. It is in seconds. So, if ya want it to check every minute, just change it to 60 instead of 1800, which is 30 minutes.
Now I placed this bit of code toward the end, right above:
/* End of file functions.php */
/* Location: ./functions.php */
Oh and my current version of WordPress is: 3.0.4
Hope this helps,
JD
