That depends. Practicing is very important, but even more important is establishing a routine you can stick to. So it won't do any good if I say, "thirty minutes a day, minimum" and you get depressed that you only did fifteen minutes the first day and then quit in failure. Focus on routine and results, not time.

It is possible to get results out of ten minutes of focused effort. It is more likely that you will make the time to put in the focused effort if you have a routine that puts your instrument in your hands every day. It is more likely that you'll stick to the routine if you are seeing results. The amount of time is not the most important factor.