Originally Posted by sinoflyer

This qualifies for TWOV. At this point, there is no point calling UA for reassurance that you won't be denied boarding at the airport. As others have suggested, have a printout of TIMATIC and be prepared to defend the fact that Japan is the the third country in your itinerary. Sad but true, but airport CS agents making their own interpretations of China's TWOV rules is something that you have to plan (i.e budget extra time) for.