Fastest way to do wanikani

The guide posted by @polv is very good and explains everything you need. I’d also recommend reading that.

However, a very distilled down version specifically for going maximum speed is:

  1. Do the radical lessons immediately upon leveling up. They all have to be at guru before you can do the lessons for the kanji that have them as components. This realistically requires installing a user script such as Reorder Omega that allows you to specify the order you want to do the lessons.
  2. Do all of the lessons for the kanji that are available until the radicals reach guru and the remaining kanji become available
  3. Do the lessons for the remaining kanji as soon as you guru the radicals
  4. Do the available vocab lessons while waiting for the radicals and then kanji to reach guru

Keep in mind that all of the levels other than the fast levels (1, 2, 43, 44, 46, 47, and 49-60) have time progressions as:

SRS Level Review Wait Time
Apprentice 1 4 hours
Apprentice 2 8 hours
Apprentice 3 23 hours
Apprentice 4 ~2 days
Guru 1 ~1 week
Guru 2 ~2 weeks
Master ~1 month
Enlightened ~4 months
Burned -

In other words, the fastest you can get the radicals to guru is about 81 hours or ~3.4 days. That means you need to do the associated reviews at the right intervals to achieve max speed.

Disclaimer I have no intention of going max speed and burning myself out, so the information above is not based on personal experience, rather it is based on the aforementioned post and understanding how the system works.