I just looked into it, IFTTT won’t work (as far as I can tell) because the pre-defined ‘events’ (triggers) don’t have planned events listed, only actual events. For example it has ‘schedule started’ as a trigger but not ‘schedule planned within 18 hours’, so there isn’t a trigger that would activate before the actual watering starts.
Not sure who defines these triggers, is it Rachio? Can Rachio add a trigger for ‘schedule planned in 18 hours’ or something similar?