I agree with Ken. Just be cautious around following a timeline for beer fermentation, especially if bottling the beer. You aren't baking a cake here, the beer will be done when the gravity is stable. All that said, I rarely take a second reading. If the beer is around where I think it should be after 2 - 3 weeks, I keg it. But then by kegging I'm not risking a bottle exploding in my friend's hand either. Patience, Jedi.