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About 3 days.

Faster if you use a kiln.

not billions of years?

Why would it take that long?

Don't ask me, I'm not the one that would suggest these numbers.

I'm pretty certain nobody has ever claimed it takes "millions of years" for mud to dry out.

Nope. They do. You know that. So, it seems like you are lying on purpose. You know what they say in the textbooks.

Citation please.