Yes, but if the clocks on earth and the other planet at rest in the same frame are synchronised to an observer (planet/transmitter) also at rest in that frame, then they cannot be synchronized as far as an observer moving relative to them is concerned. This is absolutely basic to SR. Even if you could arrange to start them at the same time according to some observer moving relative to them, they would not remain synchronized for that observer.Ok, before I go any further, let me ask this: Why do the clocks on Earth and Planet X HAVE to be out of sync? What if I have someone on a planet that is equidistant from both Earth and Planet X send simultaneous signals to both planets to set their clocks together? The signal would take the same length of time to reach Earth as it would to reach Planet X, so that both clocks would be set to the same starting time.