how long does it take to get an rss feed after content has been published?

I recently installed an RSS feed on our company forum. I did some tests and it a开发者_如何学Goppears that if I subscribe to a feed it takes at least 45 minutes before I receive the rss for published material. Is this usual? Is there a faster way to receive updates?

you can configure the time but it always depend in the client to accept it or use a fixed value

http://cyber.law.harvard.edu/rss/rss.html#ltttlgtSubelementOfLtchannelgt