It takes millions of years to make coal as the coal can not be produced synthetically and is made naturally by the fossils of different things.
The original period lasted about 60 million years. This all happened 200 million years ago, when conditions were right for the formation of coal. At that time, large amounts of toxins, like lead and mercury, were sequestered along with vast amounts of carbon during the Carboniferous Era. This "cleaned up" the environment to the extent that larger animals could evolve.
It takes millions of years and you need all your ingredients to make it
Four hundred million years
Hours or days ... It's been done in laboratories. It doesn't take millions of years at all.
It takes two hours to make it just like a fart