Gun Cleaning Product Tests
I'm guessing this is the article you are referencing. I am now going to discuss carbon solvents through the firearm cleaning perspective. (which I am intimately familiar with)
Carbon Solvents are applied chemistry, which means you are using chemical reactions. These reactions require time, heat, or agitation to work. I did not notice a time of waiting for these "tests." I have cleaned machine guns that I have run thousands of rounds through earlier in the week. Use of carbon solvents has literally saved me hours during maintenance. To speed up the time for reaction, companies could add ammonia. But ammonia can easily eat the chromemoly off the barrel if left on too long.
Now for an automotive application, the time available for these solvents would not be long and a strong solvent would prematurely wear the powertrain.