What is the impact of DWDM devices (IE: ROADMs) on the propagation delay of a long-haul fiber-optic link? Nonexistent?

So the speed of light is about 300,000 kilometers per second, but due to the higher refractive index of fiber optic cabling compared to that of a vacuum, light, for the purposes of networking, travels at about 200,000 kilometers per second; this equates to a propagation delay of 1 ms of latency per 200 kilometers. I'm curious to know, though, how do technologies such as DWDM affect this? If I have a wavelength on a service provider's network, will their ROADMs introduce additional delay to the connection? If so, by how much?