I let the beer tell me when it's ready. Normally for IPA, pale ales, wheat beer, I keg between 10 days and two weeks. At about the 7 day mark, I begin taking sample for "quality control", when it taste right, I keg it. For beer like porters and stouts, I secondary after two weeks, and let it sit another two or longer depending on the gravity, and yeast used. "quality control"begins at week three.
On my house beers that I know, well, I just know when they are done, assuming all went to plan during fermentation, and I keg it by the calander.