That seems pretty reasonable. No one doubts that achieving a high level of expertise at anything takes time and effort!The number changes for different activities. For activities like violin where the ability to practice is relatively easy the number is relatively high and for activities like skiing, sprinting or sky diving where practice is relatively difficult the number might be relatively low. But in either case, reaching the necessary amount of time to reach expertise takes a lot of effort and grit. That is the take away of his research not a specific number of hours.