Yes I need, I need my Samurai

Needs All Under Heaven. As any Ritsuryō governor who heads their house (i.e. holds the Domicile), the conversion decision is available in every start date - the only actual work is upgrading your Domicile Mansion to level 2, moving the domicile into a county inside your own governorship, and paying the decision cost. Under an hour. A natural warm-up in the same Japan run as Shōgun.