When was Lord Vishnu born?

According to Shiv Puranas, it is believed that Brahma and Vishnu were created by Ardhnarishwar i.e. the half of Shiva and Parvati. Brahma was born from Rudra or Vishnu. Other versions suggest that Vishnu, Shiva and Brahma create each other in a cyclical pattern in each aeons or Kalpa. Accordingly, Vishnu sows the seeds of a new creation at the beginning of each Yuga. As a result, Brahma, Vishnu and Lakshmi are created. Lord Vishnu is himself believed to be the sustainer and protector and is thus believed to have existed before the actual creation of the universe.