Hi there, congratulations on graduating high school!
I’m currently in college too, however I’d like to put out a disclaimer first — my workload probably isn’t as heavy as yours. Although I’m taking 23 credit hours (two of which are French), most of them are elective courses which are quite easy. As of now, due to COVID-19, many extra-curricular activities are suspended so that’s freeing up a lot of my time. I don’t work part-time too however I’m still active in many competitions (both locally — in university — and nationally).
Every day (either in the morning or the night before), I’ll make a to-do list which includes completing course work/assignments and Japanese studies; I’ve been doing this through the 勉強しましょう thread, however you can make a list in your personal device. Class usually starts at around 8 am, so I’ll wake up at 6 am due to religious reasons, after which I do WaniKani + Torii SRS reviews & lessons.
During lunch & dinner, I’ll multitask by doing WK reviews, immersing in Japanese, or studying Genki. I don’t have many classes in the afternoon, so I’ll utilise that time to work on completing the assignments I have written out in the to-do list. I’m free during the night, so I’ll do my assignments then too.
I have a study group with a few of my classmates (we connect with each other on Telegram), so we’ll work on assignments together, giving support, etc. I think this is a bonus to have to keep you motivated! Another tip I have is to ensure your Japanese learning experience is fun. That way, you don’t really need much entertainment from other mediums as you’ll have fun just by learning the language.
Don’t forget to eat well, exercise — maybe you can set around 20–30 minutes per day with an activity you like such as jogging, dancing, etc — and have adequate sleep (or at least try to… gotta be honest, it’s kinda difficult; I usually catch up with my sleep during the weekends aha) Try building a routine in which you’re comfortable with. You can trial and error and do what you feel best. It’s necessary to be flexible too; when an important deadline is coming up, you may need to adjust your routine accordingly.
Oh, another thing… I don’t really focus too much on French as I think it kinda interferes with my Japanese learning. I only study the necessities to get an A and do a tad bit of shadowing. I find that focusing on completing the assignments (for a good carry mark) is usually enough. Sorry if this isn’t what you hoped for ♂
Good luck with your studies!!!