SB 1.4.14
suta uvaca
dvapare samanuprapte
trtiye yuga-paryaye
jatah parasarad yogi
vasavyam kalaya hareh
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Suta Gosvami said: When the second millennium overlapped the third, the great sage [Vyasadeva] was born to Parasara in the womb of Satyavati, the daughter of Vasu.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
There is a chronological order of the four millenniums, namely Satya, Dvapara, Treta and Kali. But sometimes there is overlapping. During the regime of Vaivasvata Manu, there was an overlapping of the twenty-eighth round of the four millenniums, and the third millennium appeared prior to the second. In that particular millennium, Lord Sri Krsna also descends, and because of this there was some particular alteration. The mother of the great sage was Satyavati, the daughter of the Vasu (fisherman), and the father was the great Parasara Muni. That is the history of Vyasadeva’s birth. Every millennium is divided into three periods, and each period is called a sandhya. Vyasadeva appeared in the third sandhya of that particular age.