I agree that the 10,000 hour concept is just another 'rule of thumb'.The 10,000 hour number has an interesting history. Ericsson has an explanation and IIRC in general that number was picked as much as it was calculated (it was age-limited at 18 I believe ... if you used 21 year old "masters" then the number might have been 14,200 or some not-round/remember-able number).
Here is a page that has practice efforts of some rather famous and talented musicians ... they practice a fair bit :
Here’s how many hours it takes to be one of the world’s greatest classical virtuosos…www.classicfm.com
I always interpreted it as a rough estimate of about five years of dedicated study to develop some expertise in a subject. i.e. 40 hours / week x 50 weeks/year x 5 years = 10,000 hours
A university degree, an electrician apprenticeship, etc.