I don't think it works like that.  From what I've observed, it depends far more on the state of the current front page stories.  At night, when most of the stories are older, a single upvote on a New story an hour old can put it on the front page.  In the daytime, you usually need that first upvote in 15 minutes or so.<p>But it's not a set time or point scale, it's based on what's currently on the front page, how old those stories are, and how many points they have.<p>The one thing I do agree with is that after a certain timeframe, I do wish even the most popular stories decayed more quickly.