Re: Quick Scheduling For Family Members
For dynamically creating Time/Date actions, check out the Reminders
script which I believe you're already seen - it programmatically creates a time/date action. Specifically look at the line that starts "make new time date action" and look at the "absolute trigger time" property - that's where it sets the time. That script also shows you how to add/change actions associated with a time date action.
For the other you need to describe more clearly what you want them to do: edit the next sprinkler schedule that will execute some time in the future? Change a currently executing schedule? Start an adhoc sprinkler run with custom durations?