Although I haven't purchased the controllers yet, I have setup two devices on the LawnCheck website, and I'm pretty impressed!
Have you considered adding a way to "chain" two devices together? So rather than setting the first to come on at 7:00am and hard-coding the next for 8:30, set it up for the second to start once the first is scheduled to be done? LawnCheck could even take into account when the first is set to 80% and adjust the starting time of the second one accordingly.
The idea would be to complete the watering in as short as time as possible, without risking that two sprinklers will come on at the same time.
When multi-cycles are involved, it would be particularly cool if LawnCheck could run the first cycle on the first controller, then the first cycle on the second controller, then the second cycle on the first controller followed by the second cycle on the second controller. It seems like LawnCheck should be able to calculate the start times for each controller without too much difficulty.
-larry