In general that's correct, however it's not quite as simple. For latency you need to consider group velocity (not phase velocity), which depends on the waveguid

In general that's correct, however it's not quite as simple. For latency you need to consider group velocity (not phase velocity), which depends on the waveguide and frequency of the EM wave. I'm actually not quite sure what it is for electric waves, but for most photonic structures it's very similar to the phase velocity. The phase velocity is about c/1.5 for silica, but more like c/3.5-c/2 for most materials used in photonic integration. I'm not an expert on integrated electronic circuits, but I guess the difference could matter depending on application.