One thing to know is that doing all lessons at once does not necessarily lead to leveling up faster. This is because only radicals and kanji affect the leveling up (vocabulary doesn’t). Another important point is that separating your lessons in batches throughout the days does not imply that the person will level up slower either. An extreme example would be that I did Wanikani in 1 year (close to maximum speed) and I did 20 lessons a day for that year.
Also, by separating lessons throughout the days, you get a more balanced amount of reviews every day. If you were to do all lessons in 1 day, what will happen in the long term is that you’ll have days with only a few reviews, but others with a massive amount of them. Wanikani favors those with a routine, and that is made easier with a constant amount of reviews on a daily basis.
For more information about this, you can read Chapters 4 to 7 of my Guide for Wanikani 