When a fixed schedule is created we take the current average weather and build run times. From there on a weekly basis we adjust based on predicted and current weather.
I want to redo fixed schedules closer to what you are talking about and more industry standard where we set run time for historical averages in hottest time frame (usually July), then apply a seasonal adjustment to offset for the current month. As you approach July adjustment will reach zero, and then back off again as you go into Fall. A few other things we want to do like when you change watering interval, we re-adjust times, etc.
So, the current plan is to revisit these probably in Fall/Winter for next watering season and do a overhaul taking feedback we have received this year.