Before I go, I'm planning on taking 4 months off of everything to dedicate ALL of my time to studying Japanese. I have completed RTK 1 and I'm about 1000 cards into Core 6k.

My question is this: assuming I have 12 hours a day reserved for studying (and taking proper breaks), what is the best use of my time?

I'm open to hearing ANY and ALL opinions on this. I'm also concerned with what kind of goals I should set for myself at the end of 4 months. Should I just bust out Core 6k first? How should I schedule my day? Recommendations on YouTube/reality TV shows to watch?

Thank you so much.

at the start do 70 new words/day, when you get to 3k or something gradually slow down to 40/day, read all of Tae Kim/ similar grammar overview, after that get as much practice in the area that you need

I don't know what I would do with twelve hours, that's too much time to even comprehend for me. I think anything over the six hour mark and you need to start thinking about how much your brain can physically handle learning in a day rather than just how to maximise your time efficiency. A lot of people would get too tired to study any more before they ran out of time, even with regular breaks.

If you seriously have all that time free and are already at a level where you can have something resembling a conversation (some basic grammar plus 1,000 words is enough if you have selected them wisely), then I think finding several native speakers for language exchange would be a good idea. Learning new Japanese is necessary, but turning what you already know into second-nature is equally important. At least one session daily would be idea really, make it a habit.

One language exchange a day and you still have 10+ hours to spend on whatever else you decide to do, it is definitely worth the time investment. Even if you arrive in Japan having learned hardly any new vocabulary, you should have no trouble reaching a point where you can speak well. I spent 99 days getting through 90 Pimsleur lessons plus about 30 minutes a day shadowing Assimil, that got me to the point where I can fake it fairly well despite knowing relatively little Japanese.

Since writing is a thing that appeals to you, you may also consider doing a short written exercise every evening or something. In my opinion it would be a mistake to spend all that time on RTK without following it up with real writing.

I would consider what skills you need most when you get to Japan and prioritize study accordingly. 4 months isn't a lot of time if you hope to be fluent in reading, writing, listening and speaking. Of course you want to study a little of everything, but if you need to be conversant when you get there, I would spend more time on listening comprehension, shadowing and language exchange - less time on reading and writing.

Spend a lot of time reading. You need to do more than just drill Core.

If you have 4 months of being exposed to real Japanese prose then you'll be much better off when you're there. In the entire journey of learning the language wrapping your head around Japanese as it's used will be the biggest "shock", so try to go through that shock before you go. If you want to be ambitious try to finish 3k or 4k in Core and then see if you can get a full novel read before it's time.

Thank you all for the advice. Good call on the 2 hour a day language exchange, that is a good idea. I should be able to manage 70 words a day with this much time, so we'll see how it goes.