Things were heard and spoken to the next in the lineage long before it was written down. Hinduism is basically that, and very diverse, you cannot put a date on it like some "religions" which have specific "founders" or a set of prophets. Because what Hinduism is doing is taking the insights and "revelations" passed down by word of mouth and rites from one to the next from the very foundations of human "existence", at some point what was passed down was put to written script but it was heard and memorized and passed down long before it was written down. Along the way, yes certain "historical figures" or Divines appear that you could try and attribute a date/time/century/eon/yuga to. But that Figure or Divine may have a time frame but Hinduism existed before that appearance and the appearance continues what we call the "tradition" but really what Hinduism is doing is conserving those things, the knowledge, and most important PROTECTING it as much as possible on and on from past into the future into the next.
For example Krishna was mentioned. It doesn't matter the date/eon/yuga etc as far as "pinpointing the beginning of Hinduism" because Krishna didn't create Hinduism or "found it" at the time He appeared. It already existed before. Now He may have REFORMED it in some manner as required to PROTECT IT based on the circumstances OF THE TIME such as the danger from demonic governments or rulers or powers etc., but also this "reform" still contains the things that came from long before, passed down, into the future and onward. "When Krishna came" is NOT the same as "when Hinduism came".
I will tell you, the oldest City (what we think of as a city today) is Kashi in India. This is the humans first City. Now, in the modern era (though I consider the "modern" era much, much older than likely some others), those who have forgotten the past because their father and mother and teacher did not VERBALLY pass it to them who needed to listen, they will try to discover the past. That is good. But their only way, typically if they do not have spiritual powers, is to dig something up from the ground, try to figure it out and then date it.
The problem here is the nature of the Earth itself. One thing from long, long ago, a stone or gold for example, may have been picked up by ice, by weather, by wind, by humans, by birds, eaten and then cast off, many times over. It is not even in it's original place. And one area due to tropic damp climate, what was there was blown away, taken down or even totally eaten by termites, or picked away by birds, many things, while another place it was very dry, put under sand, preserved, and so on. And even more important to understand, that one place that is not wet may have been dry, and the place now dry may have been wet, and the earth moved under your feet, and what was under the sea is now not or what was not under the sea now is, and the stars once navigated by are not in the same position, and the rivers reverse direction, or the magnetic force reverses, or Brahma's Fifth Head is cut off, or a bridge is built from India to Lanka, or worlds collide.
I have no doubt, that what you may think of as "ancient civilization" - such as just use ancient Egypt as the example - that type of Civilization existed all over the entire world where humans (though perhaps less in number) congregated in any numbers. All over the world simultaneously. Because your achievements are much older than you think. It doesn't matter where you find your broken clay cups. In one place, they did not disolve - by circumstance- but mostly they did.
One other mistake is to only think in terms of Bhumi Mother Earth. Hinduism existed and exists on many other planets, universes, lokas, realms.
It is also a part of DNA.