When is Lord Vishnu\'s birthday?

The universe has been created by the holy Trinity composed of Vishnu, Brahma and Mahesh. Together these three lords describe the laws of nature and creation. The birth of the Trinity is unknown and a great mystery in itself. In some cases, it is believed that Shivji created both Brahma and Vishnu and vice versa. Since there is no hardcore evidence, the theory is controversial.
However, the life-span of Lord Vishnu spans 311.04 trillion human years and the same is one breath of Vishnu. When He exhales, thousands of universes emerge and one Brahma is reborn in each universe.