An Online Drum Video instructor I take lessons from emphasizes Goal oriented practice over Time Oriented practice. The concept being that setting aside time to practice isn't as important as the quality of the practice. Each person learns things at their own pace, some faster than others. Another teacher of mine said the hours don't matter if you get closer to figuring out what you're learning.

That all being said, putting a time limit does help motivate to achieve those goals. The Drum Instructor also says you can set daily, weekly, or even monthly goals to help with whatever you're trying to accomplish.

I suppose the article is an interesting look at how long it can take for folks to accomplish something, I get the feeling a lot of folks might get the wrong idea about what it is.