If you do around 15 to 20 lessons per day and do the reviews properly you can rush and finish Wanikani in bit more than a Year. Here is a Guy who reached level 60 in 368 days It`s a good read to understand how Wanikani works. My Journey of 368 days (+ The Ultimate Guide for WK 📖 ).
EDIT: Here are some Maths. According to WK stats Wanikani has 8974 Items including Radical, Kanji and Vocabulary. 3 years have 1095 days, but since it takes around 6 Months to burn an item lets consider 900 hundred days. That would be around 10 lessons per day for 2 and half years and the last six months should be only reviews.