End before sunrise scheduling sets the start time assuming all zones will water each time it runs, which does not happen very often with flex daily. I would wait until Rachio calculates the start time each day depending on which zones are watering before bothering with this option.
Don’t change the precip rate setting unless you know what rate your nozzles are actually putting out . This would reduce run time, but Rachio will think you are putting more water down than you really are. Your zones will dry out before Rachio wants to water them again.
I suggest start by trying a different scheduling option (e.g. start at 2 AM, or after sunset if that is OK).
I think you want to try to avoid having all zones need to water on the same day.
You can schedule a few extra waterings manually so all your zones don’t have the same moisture level, and water on different days. If you aren’t watering all zones each day, then run times will be less than the maximum.
Another option is to split your zones, and set up 2 flex daily schedules that run on alternate days. That would cut the max run time in half.