No, they obviously use the modern definition based on cesium clocks, or some equivalent. In fact, they set up long–term interplanetary communication systems so

No, they obviously use the modern definition based on cesium clocks, or some equivalent. In fact, they set up long–term interplanetary communication systems so that any civilization which had fallen and rediscovered radio could learn their language and units, so customer civilizations mostly used the same definition of a second even though their day/night cycle might be completely different.