While the idea seems sound. The amount of hours should be a variable in this case to be adjusted according to someone's own pace of picking new stuff up.
While "100" is an easy-to-remember round number, it's just an
approximation. Some fields might require ten or twenty hours to
achieve a level of medium competence, while other fields might
require several hundred hours.If the bottom line is that the more you practice the better you get (or rephrasing it, if you practice a relatively small amount of hours you will be more competent than an absolute beginner), well, breaking news from the Department of the Bleeding Obvious.