I once heard of a guy who used a popular flashcard app to learn Spanish, German, and Mandarin (in that order), spending about 4 months on each language and claiming Upper Intermediate/Upper Intermediate Plus listening comprehension at the conclusion of each 4 month round.
He built the flashcards himself using the highest frequency ~10,000 or so words from each language.
He had no family, no other pressing activities, and had a job with standard hours and no overtime.
So, he decided to dedicate 6pm to 11pm every evening to language learning, including weekends.
All he did was constantly listen to news podcasts and audiobooks in the background while he was doing flashcard after flashcard, starting 100 or so new flashcards every day and also keeping up with reviews.
If he needed to make dinner, check the mail, go to the bathroom, etc. he would take the podcast or audiobook with him.
He had a hard stop at 11pm every night, put away the app, turned off his running audio, and went to sleep, whether his reviews were complete or not. No reviews in the middle of the night if he woke up and no reviews during work. He wanted to remain excited for his 6pm to 11pm language learning every day.
He claims to have never read any Spanish (expect in school, years ago), no German, and no Chinese (he used pinyin on his flashcards I believe).
In this manner, he claims to have knocked out Spanish, German, and Mandarin “fluent” listening comprehension all in one year.
I’m sure there are others who have done similar using the Listening-Reading technique, but I found this guy’s account of what he did, especially with just flashcards and audio, pretty interesting when I read it years ago.
Then he visits Germany he will be shocked he ain’t understand a single thing 
Inspirational story 
I think there are some important lessons. I would struggle to follow this method, and could never dedicate this much time, especially to pretty much just studying flashcards, but I think that the following are more attributable to his success rather than exactly how he did it:
- he created a consistent habit. He was clearly strict in this habit, but from what you said - he started consistently at 6, stopped consistently at 11 - all that suggests that he made this a firm habit
- he did something every day, so he was making consistent progress
- he put in a lot of time, although he was studying three languages - per language it averages just over 1.5 hours a day, which is still a lot, but more achievable if you are only studying one language
- his method was consistent and standardized. I think chopping and changing methods often hampers progress (it does for me) - sometimes a change in method is helpful, but I sometimes get more bogged down in the methods than just sticking with a method consistently.
- he was excited and looked forward to his daily study - so he was enjoying the process. Clearly that is such an important in language learning, as well as maintaining motivation.
So yeah, that resonates with what most people that have learned languages successfully say is the trick to success: do something every day, create a habit, stick to a method consistently, enjoy it, and the more time that you can put in the faster your progress will be.
Your story didn’t mention what his motivation was for learning those languages, but that’s another important part of the process. He must have had a strong motivation, as I do wonder how one could motivate themselves to study for 5 hours consistently every single day…
Ha, ha, ha.
This sounds like my first day in France after being a straight A student in French at high school (i.e. Gymnasium).
My first thought was something like,
“What kind of French is that?
No one talks like that (e.g. “chépa” instead of “je ne sais pas” = “I don’t know”) at my school!”
In short: There’s difference between “fluency” and “fluency illusion”…
In 1979, we didn’t even have a remote for our TV. It was one of those click knob TV’s to change the channel. And two of the coolest shortwave radios on the market were the Sony LED and Zenith TransOceanic. Then the Sony ICF LCD series entered the market. My Dad and I went into the city and these things were $350. The guy didn’t want to not make a sale, so he said “$275”. When we declined he called us Saturday shoppers, tire kickers, and that we wouldn’t know a deal if it bit us in the rear end. We kept our cool and starting walking out of the store. I heard him say 90 dollars in an attempt to mock us. I turned around and said Sold! That radio is still in-use in my home today. I spent countless hours enjoying drift-free locked tuning of Deutsche Welle. And back then, instead of fretting over what I didn’t understand, I was thrilled about understanding sentences at first and then 45 second stretches, etc. When we went to Germany, I felt like a B1 which was okay. Lots of good general interactions with locals who did not want to speak English. We also entered quickly into museums because we didn’t mind taking the German tours instead of the crowded English ones. I do that in every country I visit, even in the US–Long line to see the free 3D nature presentation at the Polynesian Cultural Center in Hawaii–but not if you’re willing to see it in Japanese, which of course we did.