Yes it makes a difference when you then ask where a planet appears to be in the sky at this very second. What we do is to first calculate the actual location of the planet at a specific time using celestial mechanics, then when we make the last step to determine its coordinates in the sky at a specific instant in time, we add the light travel time to the planet and from its actual location, determine its apparent location in Earth's sky. The correction can be several hours for the farthest planets, but since they do not travel so fast, it is not much of a difference from their true positions. We can never, however, observe the true positions of the planets unless we use tachyons or something, and that is impossible.