Did you track your daily immersion hours during your hardcore phase?

No, never. Do I have to start a timer every time I open a browser tab with a Japanese website? Do I have to start a timer every time I open a book? Play an anime episode? Read manga? That's too tedious. Change your environment and control your space instead. I'd just aim for a constant stream of immersion that lasts all day.

It's much easier to control space than to control time.

If you change your environment then, you won't have to "choose" anything. Your environment will essentially make your choices for you.

Don't [choose to] do Japanese. Only have Japanese to do.

— Khatz

Focus on your environment, not on measuring immersion time. There are Japanese schools and courses. People go to classes, then return to their native-language environment. AJATT takes a completely opposite approach. You can't switch back to your native language because you're surrounded only by the language you're learning.

In other words, if you only have Japanese books, TV and movies at hand, immersing in Japanese is the only thing you can do. All your time is immersion time, so you don't have to measure it.

From what I've observed, people who tried measuring how much time they spent on Japanese weren't actually that good. They were so focused on optimizing their immersion that they didn't immerse.

If you discover a way to measure your progress that isn't complicated and doesn't require manual work, then you could benefit from it. What might be happening is that you're spending less time immersing than you think. The only way to find out is by measuring it. So maybe it's worth spending about a week tracking your progress to test yourself.

For example, if you log anime you watch on MyAnimeList, it will provide you with some statistics, including hours spent watching. Things like the number of episodes watched or the number of pages read can be used for tracking your progress without having to manually measure the hours.