Well, that's OK, you've pointed out another error on my part: when I went to calculate the simultaneity, I gave gamma as 0.6, not 1.66 (must've fumbled the "1/x" button on my calculator; serves me right for shooting from the hip). So the signal will arrive even earlier than I said.
Ah, well. Being a physicist means, among other things, that I make (and have made) more physics mistakes than most people.