If school and WaniKani alone are taking up all of your free time, then I’d definitely dial back a little on WK. Even if all you’re doing is school and studying Japanese, you’ll want time to learn grammar and vocab on top of kanji.
I think the best strategy is to establish a very solid daily habit of studying Japanese every single day for a consistent amount of time (if you’re going to be doing more SRS on top of WK, this is especially important, because SRS is very punishing if you miss a day). This will help you plan other things around your studies, because you’ll already have your Japanese study time set aside, so you don’t have to feel guilty using your remaining time to do something else.
How much time you choose to sink into it daily is another question. With Japanese, there really aren’t any shortcuts. Learning Japanese is a long-term goal. You’ll need to put thousands of hours into this before you get anywhere close to fluency. If you’re okay with progressing slower, you can put less time into it each day, but just make sure that you keep your expectations in check for how fast you’ll progress with the language.
Honestly, I’m not exactly sure how to advise balancing other time-consuming hobbies with learning Japanese, because I have personally made the decision to set aside most of my other hobbies for at least two years, until I’m able to reach an intermediate level with Japanese. The only hobby I’ve really kept is continuing to follow pro wrestling, which is very time consuming but also gives me loads of inspiration and Japanese immersion haha.
I have done a few other things, like I did an October drawing challenge, and I did NaNoWriMo in November, while also continuing my Japanese studies, but that was honestly not sustainable for me, and if I’d tried to do that level of work year-round, I probably would’ve burned out on at least something. So if you do try to keep a pretty demanding schedule, make sure that you’re not doing too much.
You might find that you can’t actually balance doing all of these things at once. Sometimes, it’s possible to give up some hobbies, or switch to doing the same hobby in Japanese, which could free up a little more time. I stopped playing video games (for the most part) and have held off on watching a lot of shows because I’ve been putting that time into language learning instead. But I’m very fortunate because my main hobby prior to studying the language was already in Japanese, and my work schedule is light enough, I can put a fair amount of time into both of my main hobbies (studying Japanese and watching wrestling).
How much time a day do you think you could reasonably commit to learning Japanese? And how much are you putting into WK daily, and how long does it take you to level up? Maybe we could help you optimize the time that you do have a little better.