Novella, so small time commitment.
This is unlike anything I've ever read before. Yes, there's actual time travel, but that's just a framework on which to hang a story. A really wild weird wonderful story of two post-human (!!) women (!!) on opposing sides of a war who maybe sort of fall for each other, as they fight the war. BUT! The time war is nothing like historical military wars you've heard of before.
It is SO GOOD.