Rain delay may not do what you think. I discovered this when I played with it. I thought it would give me a delay in watering after the rain sensor had activated thus giving the ground time to dry out. Not so. It seems to be a way of providing a delay in watering that is absolute. By this I mean that if you set it for 12 hours then it will not allow watering for the next 12 hours. It seems to have nothing to do with the rain sensor that I have on my system.
Maybe someone can tell me if this is correct.