Well that only half right, because beside time, there also several thing that you must notice about practice to play violin. What is practice? Basically practicing in violin mean that we try repeat to do something that we cannot do, until we get used and able to do it. And this is was one thing that we must remember, if we practice the wrong thing, so the effect was we get used (we trained) to do a mistake.
That's why i ever say that if you try to learn violin, you must if you can, get a mentor. Get someone that can check the way you play. Someone that already can play to help you to be able to do the right thing, and make sure you don't develop a bad habbit.
And other thing was, practice, it mean we try to do something that we cannot do, so we will be able to do it. We cannot call it practice, if we spend many hour doing something that we already can do. Because only doing what we can do, doesn't make us batter. But by doing something we cannot, than we can make a progress.
So every time you want to practice, ask yourself, what i cannot do well, and i want to make it right now. Maybe your intonation, or maybe your speed, well, you must have a clear goal everytime you go to practice, otherwise your practice will be only wasting your time.
Oke, maybe that was my sharing about practice for now. ^_^
Happy practicing. ^_^