A better way to state your above question would be:
1. "Does it take a lot of time to learn how to speak English in the USA?"
2. "Do you need a lot of time to learn how to speak English in the USA?"
To answer your question:
Studying English while living in the country where it is spoken is the most effective way to learn. Past that, how much you learn and the amount of time it takes is up to you and your goals.