That is one good question. The answer is it depends on many factors:
1- How much are you exposed to the language (Immersion)
The best way to learn Chinese is a total immersion i.e. to go to China and live there alone without any other friends or relatives. That way you will learn to speak in Chinese. Otherwise you will be starve to death.
2- Your level of natural linguistic ability
How fast can you pick up a new language based on your past experience? For sure, Chinese is a difficult language for most English native speaker. Hence, it really depends on your natural ability to pick up new languages.
3- How often do you practice Chinese?
If you are practicing Chinese only 2 hours a week, that won’t help. Perhaps, you can tune in to Chinese radio or watch Chinese TV to enhance your learning experience.