If one chants the exalted holy name of the Lord again and again and yet his love for the Supreme Lord does not develop and tears do not appear in his eyes, it is evident that because of his offenses in chanting, the seed of the holy name of Kṛṣṇa does not sprout.
Śrīmad-Bhāgavatam 3.11.19The duration of the Satya millennium equals 4,800 years of the years of the demigods; the duration of the Tretā millennium equals 3,600 years of the demigods; the duration of the Dvāpara millennium equals 2,400 years; and that of the Kali millennium is 1,200 years of the demigods.
Brahmāṇḍa PurāṇaBrahmāṇḍa PurāṇaBrahmāṇḍa PurāṇaBrahmāṇḍa PurāṇaBrahmāṇḍa Purāṇa