Four thousand celestial years is the duration of the first or Krita age. The morning of that cycle consists of four hundred years and its evening is of four hundred years.
चत्वार्याहुः सहस्राणि वर्षाणां तत्कृतं युगम्। तस्य तावच्छती संध्या संध्यांशश्च तथाविधः॥