It would be good to have 'finish by' schedule. I would like the system to be smart enough so it will finish by certain time or an event. For example, I've read that irrigation is supposed to finish by sunrise. So I work backwards.
It makes sense for me to have a three input fields in your UI.
First is the "Logic". Either "Finish by" and "Start on".
Second field would be 2 types of values. "Time" (clock) and relation to an "Event' ("Sunrise" and "Sunset" would be one. Another thing I can think of is "Mid-day" or "Peak sun".)
Third is "offset" (For the event). 1 hour later, 1 hour before, etc.
So this would allow the home owner to specify something like "1 hour before the sunrise, complete your watering" or "1 hour before 7am (when the kids are going to run on them) finish the spinkler".
Let me know if this helps.