Given how the SRS (Spaced Repetition System) works, there is a maximum possible speed at which it’s possible to progress on WaniKani; 6 days 20hours per level. Most people would probably say though that this isn’t strictly required and that you’ll be better off setting up a manageable routine. Doing twenty lessons per day is the recommendation I see most commonly and keeps you reasonably busy with reviews while not overwhelming you.
That maximum speed is because you can only progress to the next level when you’ve gotten the majority of kanji for the current level to Guru. When you level up, you get just over half of the kanji for that level unlocked and you must get these up to Guru before you unlock the rest for that level.
So if you look at the maths this way:
Unlock Kanji = 0hrs
Apprentice 1 → 2 = 4hrs later
Apprentice 2 → 3 = 8hrs after that
Apprentice 3 → 4 = 24hrs after that
Apprentice 4 → Guru = 48hrs after that
So the total levelling time for first batch = 3 days 12 hours
You then unlock the next batch and must spend 3 days 12 hours again on those
I wouldn’t be overly impatient, because the reviews will start to come in more frequently as you progress, because…
You’ll see items you have at Guru 1 after a week. Then again after two weeks. Then again after a month. Then again after four months. So the longer you progress, the more reviews you’ll start to see coming back from the earliest stuff you did. Once that happens, you’ll have reviews galore.