An important point is to understand what is meant by fluency. Personally, I believe fluency is the ability to interact in most everyday contexts without major communication obstacles. While proficiency is the ability to understand and reproduce as faithfully as possible the communicative strategies of native speakers.
Do you agree with these definitions?
Another key factor is exposure to language.
You certainly cannot improve your Italian while you sleep (despite some people claiming it is possible). To achieve a level of fluency in Italian you have to be exposed (almost) daily to the language.
If you already live in Italy then you are bound to be exposed. If, on the other hand, you live abroad but study Italian you already know that nowadays thanks to the Internet and all the multimedia materials we can enjoy, it is really very easy to listen to songs, watch videos and movies, read all kinds of news and updates, and of course follow your favorite creators on social media.
I for one, when I watch a movie on TV, I always try to watch it in the original language (in English or in French). And when I work as a tour guide of course I am immersed in these two languages all day long.
So, the question is how much exposure do you get to the Italian language every day?
A foreign language is like a sport. If you were able to run a marathon five years ago, you may not be able to do it today. Even with Italian, it's a matter of training.
The problem is that it involves a completely different kind of organization than passive listening. To practice you need a social context, a professional or personal need. One thing, however, is certain. There is no better teacher than practice.
So another question for you. How many hours a week do you practice Italian?
The last aspect I will consider is personal inclination toward language learning. There are people who have to learn Italian, who are obliged by various circumstances to use it but who have never opened a grammar book in their lives.
Then there are the foreign language enthusiasts who would spend hours reading the rules of the subjunctive (and who also know how to interpret them well).
The Italian language is not always a passion or a love story. Sometimes it is a necessity, and active learning can be experienced as a hardship by many. And that can make a big difference in terms of the time it takes to achieve fluency.
Certainly not (although it would be beautiful). But surely a week can be enough time to start enriching your Italian vocabulary. Wanna bet? Come try my advanced Italian courses for free for a week. No credit card required!
As you can see, time becomes a very subjective issue. That is why my online advanced Italian school is a subscription school. You can decide to stay as long as you want, with no payment constraints. On average my students stay at least six months and believe me they leave with a much richer Italian. But some stay only a month and delve into a particular topic.
What about you? Give it a try for one week! 
