It's a hard question you are asking. Flex is amazing because it tracks both inputs (water put down) and outputs (water used) to figure out when watering is needed. To do that, however, requires some thoughtful setup (if not measurement).
First off, your historical approach is not aligned with watering best practices. Your yard conditions alone dictate the length of a watering cycle. If, for example, a deep watering for one of your zones takes 25 minutes, it should take 25 minutes whether it is in the spring or the summer. The difference is that you will water less frequently in the spring, not for shorter run times. In order to use the Rachio to its potential, you must accept the "deep watering" philosophy. In fact, you might even find that you should be watering less frequently (but for longer) in the summer. Be open to that possibility.
That said, here's a thought for you: try setting up a flex daily schedule using defaults and see what the system shows for watering times. Specify each zone carefully with regard to vegetation/slope/soil/sun (use default for root depth and 50% for depletion). That should be a good starting point for the usage side of the equation.
On the input side, maybe start with a default 1"/hour for your spray heads, maybe 0.5"/hour for rotors, adjusting up/down based on what you know about them. For example, a zone with half-circle rotors puts down water at twice the rate of a full-circle rotor.
Now, take a look at your Flex Daily schedule. Open it up and see what durations are showing for watering. If they align with what you think they should be for a deep watering, then you are all set. IMO, do not tweak these watering times using the +/- buttons; you are better off changing the input assumptions that drive the watering times per zone.
If you'd like to watch how the system calculates water balance, now disable this new Flex Daily schedule, leave your interval schedule running, and come back to it in a week or so. Reenable the Flex Daily schedule and you can look at moisture levels zone by zone. You can get a sense of how your historical knowledge lines up with how the system is measuring moisture balance. Once you are comfortable it is working "properly", you can enable the Flex Daily schedule and let it take over.
Ultimately, when you have some time on your hands, you would well be served to figure out how much water your heads are actually putting down. You'll already have the consumption side of the equation covered, and this would be the final piece to get the Rachio system working to its fullest potential.