The longer we stay on the German model, and not on the British one, the value of the debt held by Japan and China will diminish in real terms. And with it, will also go their desire to continue to prop us up financially. They will lose their “stake” in the US economy. At some point, they will write off that debt as worthless, and the dollar will cease being the world’s reserve currency.
Walking away from, or diluting out through money printing, the Japanese and Chinese debt will not benefit the U.S. Beyond the Greenback losing international credibility, the gain from 'default' will still leave $200 trillion or so of unfunded liabilities, all of which are either literally or effectively indexed for inflation (SS, Medicare, Medicade, Obamacare, etc.). Those who think that they are being smart about this will be proven incorrect. The denouement will likely occur in a similar time frame to your German example: five years or so.
The five years of the German notes is what hit me when I read about it. That seems to be the most common term of our Treasury notes that are being floated. So yes, I would go with your five years.
By the way, I read about his in Volume 1 of Hew Strachan’s “The First World War.” He devoted a good of that volume to how the war was financed. It was pretty dry, but in the end well worth reading.