Is there a reason why rachio seems to prefer to water all zones on the same day with flex daily? The schedule it created leads to starting to water at 11pm the previous day instead of staggering zones across all days of the week. I ended up creating multiple schedules for groups of zones that are restricted to a couple days a week (odd and even still led to too many zones in a day) to try and force the issue.
It seems like creating a rotating schedule would make the most sense.
And someone else complained because while they all started on the same day, they got out of sync. 
I agree with you that having them staggered results in less of each day (or night) being used for watering. But you may not know that even if only one zone is watered, your “End By” preference will still result in beginning to water at 11pm the previous day! I START my watering at 5am, and it usually ends by 8 or so but can water as late as 11, which I accept.
You have a very long watering time; are you watering a Drip zone during the same time? If so, try moving that to late morning or during the day, as it wastes very little water.
Oh - to answer your question: When you first start using Rachio, it assumes certain moisture levels, and will usually water ALL ones the first time, and for quite some time. You can do a Manual watering of zone or 3 in between, which would force them to water later, so not all are watered on the same day. But a lot of people want to limit the number of days their lawn will be wet, so have not requested a similar feature.
If all your zones are same settings (sunlight, soil comp, crop coeff, water available, root depth, etc), then they will all run out together. All get set to 110% at a good rain, then water % decays the same everyday they all get to 0% on same day.
As for the timing of when it starts watering, I complained about that because it doesn’t matter if its doing all zones, or 1 zone, it always starts at same time, which if you are set to “end before sunrise” it takes -. It doesn’t consider actual watering time for start.
Yeah, it was a little frustrating that it would try and start at the same time irrespective of how many zones were scheduled. What I ended up doing is breaking up my zones into multiple schedules. The number of schedules set to run will dynamically adjust the start time although it means that the schedules run in serial instead of staggered. I ended up putting about 3 zones in a schedule.
Why don’t you describe how you set up your schedules and times? It might help others with similar situations.
Mine started out like that as well. But as I refined my areas according to the slope and sun exposure, I noticed the soil moisture started depleting at different rates and now, after a few months, Mine splits into about 4 different watering days as needed. As someone here said, if you have all your zones setup exactly the same, you should expect that they will stay on the same day. But if you have different slopes, vegetation types, soil types, and sun exposure, they should start watering on different days at some point.