score:1
It seems mostly safe. Usually 3 hours are enough. Some months ago we had a problem with Pakistan, so most airlines should not flight over it. OTOH I assume the plane will flight mush more north.
In any case, from FlightRadar24 flight CA950, it is often on time. Few times just less then 1 hour delay (and twice with 1h30 delay). So it should be feasible.
But travel is about unforeseen circumstances, so try to think a plan B (do they have later flight to Japan? Prepare the alternative: it is simple to discuss, if you have already some ideas). Get on your cabin luggage also stuff for one extra night (and day).