I think that is a difficult question to answer because it depends on many factors.  Obviously, the more time you devote to something, the faster you will learn it.  Taking lessons daily with a certified teacher will result in much more rapid learning than working with a language partner once a week.  If you have the ability to use English in you daily life, your aquisition will be quicker than someone who is the only English student in his city.

It took about 5 years for me to learn enough Spanish before I felt honest about saying I was bilingual.  I could understand and communicate long before that however, (probably at about 4-5 months).  At first it seemed that I would never learn, but all of a sudden I began to understand one thing, then 2 things, and then it was like a snowball rolling down a hill - I picked up speed and never looked back.  I have been speaking Spanish for almost 19 years now, and I still learn new words every day.  

My children are bilingual from birth and they correct my Spanish and my husband's English all the time!

"Don't judge progress by the mistakes you are still making; judge it by the mistakes you don't make anymore"

That's a good point and I think the best way to stay sane while learning another language. I'll make a mental note of that. 

It sounds as if you are on the right track.  I can understand what you are writing, and you are putting a great deal of effort into learning.  Only you can tell if you are understanding more than before and if you are able to speak more relaxed and understandably.  Don't judge progress by the mistakes you are still making; judge it by the mistakes you don't make anymore!

 Mininmum three months, maximum one year

    Moreover,   given the fact that you are using   advanced vocabulary already, 

and with some guess as to your current ability,  I would say that you have already "learned English".

 All that remains now is for you to advance   your current level to a higher level.

  Of course,  you can go about your continued learning by some, dull or   tedious    method.

I have seen in my years of tutoring English, that many students will bypass  effective methods of study, and adopt  an unfocused or broad  approach that delays development; but then,  it is like the old saying we were taught as kids in the USA. It goes like this.

  "It's Like the Man---Who---Kissed---The---Cow;  You pay your money and make your choice."

 There used to be a  "fair"  each summer or fall in the farmlands of the United States.

There would be  many booths selling many things. To raise money for some charity or social  organization,   there would be a booth, and in it there would  two Things.   A  COW and a young GIRL.

The sign would say;   "Kisses----for----$1:00"

    So,  if a man thought the GIRL  was not as pretty as the COW, he paid his dollar and kissed the COW.

    So the student of English is like the person going to the Fair.  He can choose from many things  to spend his money, or to choose a course of study or a language partner.  Nobody forces anything.

You make your choice.