You’ve heard of realtime stock quotes. Nearly every finance site has those. Now Google Finance is adding realtime news streams. If you go to its market news page, the stories will update automatically without refreshing the page, kind of like updates on FriendFeed but not as frequent.

Looking at it now, new stories are updating only every minute or two, so I’m not sure how useful this is going to be most of the time. But when a stock-related story is breaking, it could be very compelling, giving you a sense of how quickly market information is reported.

When new headlines break every 10 or 15 seconds or so, it becomes a new way to consume news. You can sit there and literally watch the news as headlines scroll down automatically.

Perhaps that is why the news stream will only be turned on during trading hours. It switches back to the static news page 90 minutes after trading ends in the U.S. and starts up again the next morning 90 minutes before. Although it seems silly to me to turn the feature on and off. If the page isn’t moving, that simply means no news is breaking. People will figure that out. This is just becoming the way people consume news, whether on Twitter, Facebook, or news sites. We autorefresh headlines on TechCrunch, for instance.

You can’t be half-realtime.