https://www.gamespot.com/articles/ni-no-kuni-2-story-length-heres-how-long-it-takes-/1100-6457506/

Ni No Kuni 2: Revenant Kingdom is coming this week, marking another sumptuous RPG from Level-5. Like the first game, there's no shortage of things to do in this Ghibli-inspired adventure, and role-playing games are known for their lengthy playtimes. Now we have a better idea of just how much time you'll put into this trip through Ding Dong Dell.

Our Ni No Kuni 2 review said the game lasted roughly 35 hours, which included a handful of hours devoted solely to developing the kingdom. 100% completion could be roughly double at 70 hours.