It will depend on how fast you go, but usually between 1 to 2 hours. Another thing to consider is that the kanji in the first 30 levels are much more frequent than the kanji in the last 30 levels, so it might be worth considering doing the first 30 faster than the 2nd.
If you’re considering using Wanikani, I recommend reading my guide. It will teach you pretty much all you need to know about the platform
