I believe that to learn Spanish is easier than to learn English. And if study systematically you ll get progress indead. But I think it ll require lots efforts anyway and combination of ways to learn it... I mean to study grammar and watch video, read texts and communicate with real people...

And of course in 90 days it won`t be fluent)), but it ll be on the good level, let say :)

What's your definition of fluent Mike?

With my own personal definition, there's no way I could ever do it and I think there are few people who could if any, but you probably have a different definition. 

I believe it's very possible depending on your approach. I practiced every day for 1 week just speaking with friends. Asking them questions like, '' What does this mean? What does that mean?'' And by the end of the week I learned so much. My speaking and comprehension improved significantly. There's this guy named benny lewis who learns in 3 months, and he gives some really helpful tips and motivation.  You should look him up. 

What toô me most of the time, was to understand the difference between the verbs of " to be" , ser and estar and use them propperly. But after 3 months, it was ok, I was speaking spanish correctly, understanding the professors and the classmates and doing the exams

As a french dpeaker I did it. But I was living in Spain and I was forced to master the language very quickly, cause in the school everything was in spanish and I jad to succes my exams