How long it takes to learn Chinese up to a level where you can do business negotiations in Mandarin depends very much on how you study it. One very important factor is that for Chinese, shorter and more intensive courses work better than longer and less intensive ones. The reason for this is that when you have longer breaks between classes the probability that you'll forget what you learned is much higher. We have had students who made it from zero to HSK 5 within two years, whilst running an international company and being on business trips almost every second week. Our advice is always to first define a target (where do you want to get to), identify your resources (time, motivation, budget), and then let us help you create a structured plan.