Quick answer: a practical fiber optic latency estimate is about 5 microseconds per kilometer one way, or 0. 010 ms/km, before adding transceiver, FEC, switch-hop and queueing delay. Temporal delays or latency in optical fiber refer to the time it takes for a light signal to travel a certain distance from the source to the receiver. Despite the high data transmission speed, the signal does not propagate instantly and requires time to cover the distance. When transmitting over. Latency is a term that is used to describe a time delay in a transmission medium such as a vacuum, air, or a fiber optic waveguide. Fiber Length: Kilometers (km) Miles (mi) Meters (m) Feet (ft). Once the true velocity (v) of the light inside the fiber is known, calculating the latency (delay time) is a simple kinematic equation: Time = Distance / Velocity.