Imagine a source of oscillating magnetic field, say 10 Ghz. Now change in a magnetic field propagates at the speed of light, assuming a vacuum. Consider point B to be 30 cm from the source. The change in magnetic field will take 1 ns to reach B. Does this mean that B will experience changes at 10 Ghz but delayed by 1 ns? Is my inference correct or am I wrong?
In general, yes. Note that in the design of extra-high frequency comm links and circuitry, the propagation time delays and associated signal phase shifts have to accounted for, which makes the circuit designer's job much harder. This is especially true when designing computer component layouts for machines that run at GHz clock rates but less of a worry when dealing with wireless signal transmission.