First detail: Liu has a diplomatic wrangle between Japan and China over who has exploration rights over what was then the Japanese puppet state of Manchukuo. In fact, it's pretty clear that any reasonable extrapolation of current international law and practice would conclude that Japan would not have a leg to stand on, having recognised the People's Republic of China as having jurisdiction over the present day site since 1972 (coincidentally the same year as the UNESCO convention to which both are party, China since 1985 and Japan since 1992). No doubt a rhetorical case would be made in internal Japanese media commentary and political debate on the issue, which would then be reflected inaccurately in international coverage especially in China and America, but the legal situation is crystal clear.
Second detail: Liu's scientists quite deliberately choose to send only victims' relatives rather than professional historians or journalists. The point of this in the context of the story is to illustrate the flawed decision-making of the central characters, under the awful pressure of an awful history. But it's unrealistic from many points of view, particularly that of the victims' families. Having been involved around the edges of a number of such situations, what I observe is that victims want a) the opportunity to testify and to tell their own stories and b) independent documentation as a confirmation from an authoritative, possible even neutral source that the evils to which they were subjected actually happened. What Liu's scientists offer doesn't really satisfy either of these requirements. There are other reasons to find this plot element unrealistic - would the Chinese government really allow American scientists such a free hand in choosing the people who would experience the time-travel technique? - but for me the killer is that I can't see that many of the people most concerned would be really attracted by this approach.
But the big point is this: I'm not sure that a story about time-travel is really an appropriate or tasteful way of dealing with atrocities like Area 731. I have nothing against the principle of being educated while I am entertained, but I think that there are also boundaries that can be crossed and have been in this case. I felt the same about Terry Bisson's Nebula-winning story "macs", which took a real-life tragedy and monstered the victims' relatives to make a point about capital punishment; though I agreed with the point, I thought it was done in very bad taste. Back at Eastercon, a panel on the potential range of settings for Doctor Who stories agreed that the Tardis can never visit Auschwitz (see also Rebecca Levene on "Let's Kill Hitler"). I would add that on screen it has never even been to Ireland. No doubt like many other readers, I learned about Area 731 for the very first time from this story, but I fear that presenting those awful facts in a work of speculative fiction potentially undermines their importance as facts. So while I applaud Liu's detailed research and imaginative transposition of the events of Area 731 into a narrative of scientific research and personal tragedy, I won't give it the top vote on my Hugo ballot.