What is the maximum interval setting for a fixed schedule? I have some zones that need water once a month, but I read somewhere in here that the maximum interval was 21 days.
21 days is currently the largest interval. You could build an IFTTT recipe that only runs a disabled schedule once per month.
I now own a Gen2 8-zone device.
I may try an IFTT solution at some point. But for now, I don’t see how to set up a fixed schedule with an interval longer than one week.