Children of Hurin to be Published

It seems that there is going to be a new Tolkien book about elves and dwarves that has never been published before. I wonder in what age it will be set in?

Christopher Tolkien has spent the past 30 years working on "The
Children of Hurin," an epic tale his father began in 1918 and later abandoned.
Excerpts of "The Children of Hurin," which includes the elves and dwarves of
Tolkien's "The Lord of the Rings" and other works, have been published
before.