It's pretty hard to say how long they usually take because the fossil record from millions of years ago is difficult to date with good accuracy. For example, I don't think we can say with good confidence whether the asteroid that hit us 66 million years ago killed a large fraction of all living creatures within a year, or whether it took thousands of years or longer.
The sources in the Wikipedia article seem to disagree with you on that. Perhaps you want to add your sources to the article and reword it with less strong language.
