In Malcolm Gladwell's book Outliers, what is the magic number for true expertise?

In Malcolm Gladwell's book Outliers, he claims that the magic number for true expertise is 10,000 hours. He supports this claim through a series of case studies, in which he examines exemplars from across several fields, such as Computer Sciences or music. In each case, he calculates an approximate number of hours that these exemplars were able to spend practicing based on their recollections, the recollections of others, and on recorded events. His findings are astonishingly similar, despite the dissimilarities across his cases; each of these incredibly successful case studies managed to practice for approximately 10,000 hours before becoming an extreme success in his or her respective field. Gladwell's findings substantiate his claim that while talent does contribute to success, talent must be complemented by practiced skill in order to lead to success.