One thing for certain is that Vedic literature has a propensity for grandiose numbers. Unlike most of the polytheistic theologies discussed on these
boards, Hinduism is a living, evolving system with c.800 million followers. Meaning no offense to this profound and immensely important belief
system, it should be noted that we're talking about poetry generated at least 3,500 years ago, and encoded in known written form over 2,500 years
ago. There's definitely room for multiple interpretations and opinions regarding the Vedic time system do vary.
My orientation on the subject is largely the belief that the mythological systems of many world cultures, particularly the Indo-European line, are
misunderstood astronomical allegories. This means that a
literal interpretation of Vedic scripture is not likely to provide us with much hard
data to work with. I haven't by any means read all of the Vedas and of course what I have read was a translation, but these materials are available
to all of us, at our fingertips:
The Vedas
If we separate from the religious belief system and look at the lengths presented for the Yugas we find that the Kali Yuga is 1,200
Deva years
long. Each human year is described as just a day for the Devas, in a 360 day per year system this makes the length of the Yuga 432,000 human years
long, that's the source of those numbers. Deva years=God years, but if we are reading Indo-European deities as allegorical figures representing
celestial figures and bodies then we can not really take much immediate stock of the hyperbolic descriptions of Deva years. If we add up the lengths
of the various Yugas in Deva years we get 12,000 (4,320,000 human years). As my above link and quote show, the Hindu saint Sri Swami Yukteswar
explained an enigma between the value of 12,000 years and a statement in an early Veda attributed to Manu that the Four Yugas equaled 24,000 years,
diagramming how the 12,000 year period represented the ascending or descending half of the larger cycle.