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.