How long does it take to understand Japanese anime without English subtitle?

some words are easy to pick up.

but really you just need to watch to see what happens

I've watched 1k+ anime and with almost no study of the Japanese language, and at this point, I could watch anime raw, as in without any subtitles, and still get the gist of it. That said, it would also depend on the anime. Anime like Naruto and OP, meaning shounen anime, would be easier to understand as opposed to seinen anime, as the language complexity would differ on account of the different demographic that the anime aim for.

A complete understanding of any and all anime would however, require extensive study of the language. In other words, you'd need to be fluent in Japanese. Even if not in reading it, at least in speaking it.

Now, with the amount of anime I've watched, it most likely wouldn't take more than just a few months at most to reach a level at which I can fully understand raw anime. For someone less experienced, it would likely take quite a bit longer, but actual study of the language, coupled with extensive anime-watching, should reduce the time required by quite a bit, though it would also depend on your own capabilities.

To understand such *correctly*

you need to have advanced fluency in Japanese.

Why: because slang and various dialects are both common features of Japanese anime.

So: in fact you DO need "advanced japanese"

not "advanced" in the sense of academic vocabulary

but "advanced" in the sense that you need to be fluent not only in standard Japanese but also in popular slang and in the ability to identify dialectic variations and the connotations associated with such dialects.

"coolguy11," more like "Weeaboo11"

You don't magically wake up one morning and suddenly know a new language. You want to watch anime without subtitles? Learn Japanese.