With the length of the duty being three years during the Heian period, it was a large burden on samurai in non-capital regions, and MINAMOTO no Yoritomo reduced it to half a year, being further reduced to three months in the middle of the Kamakura period when the samurai side became more influential than the kuge (court noble) side.
地方の武士にとっては負担が大きく、その期間は平安時代には3年勤務であったが、源頼朝が半年勤務に短縮し、公家に対して武家の優位が確定する鎌倉時代中期になると3ヶ月勤務と大幅に短縮された。