How Often are Trend-Topics Updated?

In Twitter's support site I found the phrase:

"The list of trends changes freque开发者_开发问答ntly based on what is most popular right this minute" http://support.twitter.com/entries/101125-about-trending-topics

Does this actually mean that we can't get updated trend-topics in a shorter period than a minute?

Does this mean a topic that is very active for a minute could appear in a trend-topic list?

Thanks.

---

As far as I know Twitter has never said how often the update the trending topics. It may just be as simple as when new topics trend the trends get updated. For performance reasons though parts of their system are sure to be cached for limited periods of time.