Hello Knighty,
You have the EtherRain 7P controller so you don't have to worry about control of the master valve through the LawnCheck scheduler. With the 7P the relay that controls the master valve closes automatically when a cycle is run. This causes power to be sent to the master valve thereby opening it. This assumes of course that the master valve is connected to the terminal indicated on the label. The relay automatically opens (thus removing power from the master valve) automatically when the cycle has completed.
Also, with EtherRain 7P you can control a maximum of 7 zones and any value entered in zone 8 in your LawnCheck schedule is ignored by the controller.
Hope this answers your question.
Jim