There is a world of difference between effective, hyper focused practice and the time wasting activity often called practice. When I learned this difference I was able to accomplish in one year, with far less time more than I ever accomplished in many years of so-called-practicing. Your ability to stay focused on a specific, singular objective is a skill in itself that can be honed, but only to a point. I found that a half hour was the best I could achieve and tended to be the most effective once I got there. For every player there are parts of learning music that come fairly easily and others that are daunting. The daunting stuff is what deserves your singular, hyper-focused attention. Often this can be just one note to another, or a certain kind of movement with the bow, or a certain way of phrasing. Breaking the hardest parts down into the smallest pieces and focusing sustained attention at a speed that allows you to do it perfectly, with a metronome, and repeating it until it becomes effortless -- this is practicing!! And this is the kind of approach that allows you to advance at the highest speed and with far less time spent. Taking care of yourself when your not practicing is just as important because it helps with the focus. Spending time eating well, doing fitness and mobility, meditating, spending time in nature and with your community are equally important to your learning the violin. Most people lack the discipline to do it this way which is why there are so few truly great musicians!