There is no definitive answer for how long it takes to learn Hebrew. It depends on several factors including motivation, previous knowledge of Hebrew or other languages, innate ability, study skills, resources available etc. If you’re a native English speaker you’ll undoubtedly encounter many Israelis that will switch to English in order to improve their English. It’s a known problem that native English speakers who are serious about learning Hebrew face.
What is in your control, however, is how much you study, how intensely you study, avoiding speaking your native tongue, and the environment you put yourself in. I know many people that would be able to speak Hebrew today if they would have immersed themselves in an all Hebrew speaking environment for an extended period of time.
When answering this question, some people emphasis that the younger you are, the faster you’ll learn. As a broad unspecified statement, I disagree, something I’d like to explain in a different post in the future. At the end of the day, you can’t do anything about your age but control how much you study, how serious you are, how much you avoid using English etc. So take advantage of the Hebrew learning resources available today and keep studying Hebrew.