Suiko period

The Suiko period was an era of 25 years during the Asuka period of Japanese history. This period overlaps all but 7 years of Empress Suiko's reign (604-628) or it is used as a synonym for her reign (593-628).
Calendar.
The adoption of the sexegenary cycle calendar ("Jikkan Jūnishi") was a significant event in the reign of Empress Suiko. This pre-dates the system of which was started in 645.