A lot has been written about the 10,000 hours it takes to be at the top of a competitive field. A more relevant question might be "how long does it take to reach a reasonable level of competence in anything?"
In this TED talk by Josh Kaufman, he argues that it takes just 20 hours - 20 hours of deliberate practice. Due to the law of diminishing returns, there's a sweet spot. For a small amount of time you can get great gains.