Too little time, at least 3-4 times a week, gain muscle and eat more high-protein beef and eggs, four eggs a day, more meals, 6 meals. In fact, if you are in a gym, you'd better ask a coach to practice. As for how long, it depends on your physique. A good month will be 10 kg, and a bad month will be a few kg or even none, but the muscle quality will be obviously improved.