How long does it take to learn German on a medium/semi-advanced level?

This obviously depends mostly on where you’re from, what’s your native language,etc. , in my case I’m from a Slavic country in East Europe, however as you can see I speak English relatively good, I managed to learn Russian in just 2 years to a advanced level by mostly just watching movies and series instead of studying grammar books,etc. (though that’s related to me being slavic and languages being very similar), so if I wanted to learn German from scratch, how long would it take me if I actually studied instead of just watching tv like I did with Russian?

I had German in my middle school and I learned some basics, numbers, my name is, I’m x years old and things like that, but I’m still not even at a A1 (lowest) level.

The U.S. Foreign Service Institute says 750 class-hours (30 weeks with 25 hours of class per week, plus 3-4 hours of self-study per day). That is for a native speaker of English.