In the Puranas the ancient Vedic histories there are statements like: The contemplative, the charitable, the dispassionate and the consequent reach a higher abode that is free from affliction above the material realms of the earthly worlds, the heavenly kingdom and the nether regions.
It is known that above the three planetary systems Bhur, Bhuvah and Swah, the planetary system of Maharloka is far superior to the Earth; but if periodic destruction is anyway applicable to all material planetary systems then what is the special distinction. Anticipating such a question and in order to convey that existence on Maharloka lasts for a long duration compared to the much shorter duration of the three previously mentioned lokas or planetary systems being Bhur, Bhuvah and Swar below it. By showing that in each day of the life of Brahma which equal 4 billion, 320 million years and who lives one-hundred years according to this time scale, the material manifestation of the three worlds are created and on each night in the life of Brahma also equalling 4 billion 320 million years the three worlds are dissolved again. Both together total 8 billion 640 million.
Such is the proper method of computing time. One year of time on Earth equals one day and one night of the demigods. Computing further in gradation for them and Earth it can be tabulated that one Maha Yuga equals 4,320,000 Earth years but for the demigods that is only a durarion of 12,000 of their years. 1000 such Maha Yugas comprises Brahma’s day and another 1000 Maha Yugas comprises his night. Only those who understand time in this frame of reference are actual knowers of day and night. Those beings whose knowledge is restricted to the rotations of the sun and moon are not knowers of day and night for there knowledge is limited.
The word yuga in this verse is referring to a Maha Yuga refering to the four yugas of Satya, Treta, Dvarapa and Kali equalling 4 million 320 thousand years. Otherwise combining it with sahasra-yuga would have no relevance to Brahma’s day and night. The Vishnu Purana states: Brahma’s day consists of 1000 Maha Yugas. The name Brahma also denotes the inhabitants of his planetary system of Maharloka as well.