It was implemented with such a short notice because the Meiji government wanted to avoid paying its officials monthly wages, whose system was introduced after the Meiji restoration, 13 times a year (as the coming year in the old calendar had leap June).
この年の急な実施は明治維新後、明治政府が月給制度にした官吏の給与を（旧暦のままでは明治6年は閏6月があるので）年13回支払うのを防ぐためだったといわれる。