Unit 731 was garbage science. About the only thing worthwhile that came from that was learning how better to treat hypothermia. Most of their experiments boiled down to “If we do terrible things to people, how much will they suffer?” with the answer being “A lot.”
It doesn’t take live experiments to learn things like surgery without anesthesia is less effective, or that not treating people infected with horrible diseases causes them to die in agony.
The Martian and Project Hail Mary are some of the best sci-fi-of-tomorrow books I have ever read. Maybe not a single day, but neither are overly long.