Since it is an international itinerary, each connection should be allowed 24 hours. I can see why you would ask, but the fact that you are connecting in IAD between two domestic flight won't take priority over the fact that the whole ticket is governed by the international rather than domestic rules.

This being the case, there's no reason why you shouldn't be able to upgrade the whole thing using 30,000 miles NRT-SFO-IAD-ORD. Since you will have an overnight in IAD, it would be a good idea to have the agent who sets up the upgrade to make a note in the "United Field" that one upgrade award supports the upgrade all the way through to ORD. This way when you check in at IAD and they ask, "how will you support this upgrade?" you can tell them that it's already supported and to check the notation in your PNR.

In a recent experience for me with exactly the same issue, this was how things unfolded, and it turned out fine. Just make sure to get an agent who seems to be on your side when you try to set up the upgrade and get the notation put in. This would be a prime case where I might hang up and call back if I felt the first agent I got wasn't really into the whole thing.