There are, the authors estimate, 150 Russian remote nuclear launch sites and 70 in China, approximately 2,500km (1,550 miles) from the nearest border, all of which could be reached by US air-launched JASSM and Tomahawk cruise missiles in a little more than two hours in an initial attack designed to prevent nuclear weapons being launched.
Emphasis mine, I’m pretty sure even Russia can notice hundreds of cruise missiles are heading directly at their silos and figure out that this looks like an attack on their strategic nuclear arsenal in two whole hours, given that ICBMs take around a quarter of that from launch to impact.