As the PP said, the lights along Route 66 in Carsland come on at dusk. So it's not really a set time, but varies with the onset of "dusk". You're best bet is to ask a CM along the route; they can usually help you.
Skimming some recent Holiday time threads seems to indicate that the IaSW Holiday Lighting ceremony happens after sunset, but may vary depending on the time of the parade. Again, you're best bet is to ask the CM at Guest Services when the ceremony will be for the day you are there. At this point, I would guess that it's going to be somewhere between 5:00 pm and 5:30 pm.