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. Conversely, if an engineer requires a specific time. Accurately calculate the propagation delay and total latency in your fiber optic network.