God created the earth in six days. Only six 24-hour days. Metaphors don’t count if you are a Biblical literalist. Nothing counts, except for the words of the Bible, as translated into American English (creationism is a distinctly American phenomenon).
If the Bible is taken literally, then the only things that happened in the world happened in the corner of the world where Biblical events happened – what is now the Middle East. (There was no “rest of the world”). Using that criterion, Irish Archbishop James Ussher counted all the Biblical begats and concluded that creation happened in 4004 B.C.E. But he came up with that in the 17th century – a time known for deep scientific knowledge.
I’m not sure if any/all/some creationists adhere to that date, but they certainly don’t allow for a great deal of time from “let there be light” to the appearance of horses with chestnuts.
As an apostate of whatever religion I was raised, but someone who is very interested in the history of all religions, I personally view the Old Testament as something that began as a Mesopotamian myth and then became a mythologized history of the Israelites, that grew progressively more “historical” with successive chapters. I recommend “God: A Biography” for a wonderful treatment of God’s character evolution in the course of the story – from sex-obsessed, to law giver, to largely absent at the end.
Genesis is a lovely poem about evolution – first the universe, then the land, plants, animals and humans. It’s actually quite accurate in that sense (except for compressed timing and the two conflicting male and female creation myths), which is wondrous in itself, given the lack of scientific knowledge of the time.
As with many myths, the Biblical stories hold grains of truth. For example, scientists found a real candidate for the Biblical Flood story in the Black Sea around 5500 BCE – well within the memories of the Biblical story tellers who got it from Mesopotamia.
So, I don’t denigrate the Bible as a source for interpreting scientific evidence. But it’s just one source. Not the sole source.
As for horse chestnuts and the OP, I would advise anyone to avoid discussions on any subject with literal creationists (not the “God is the engineer who formulated the equations (Pi excepted…) that fired creation” types – I’m kind of one of those myself). But the “God created everything in six days” types. Though evolution has it’s holes, creationism is a hole. Why would God leave us all this scientific evidence of evolution? False clues to test faith?
Tell them your chestnut theory and leave it at that. If they are rude, say “sorry, I have work to do. It was nice chatting” and go on your way.