First, I would recommend Flex Daily over Flex Monthly. I think it does a better job. And with the newest release, unless you specifically want something to water at a different time, you can mix all the zones into one schedule.
In my case, even though I can put everything in one schedule, I still have 3 separate schedules. One schedule starts my grass watering around 3am so that I know it will be done before sunrise (I set this up before the new “before sunrise” option was added in). Then around 8am I water a few annuals. No scientific basis for this, but if the water is going to be on all the leaves and flowers, I like it to not be sitting on them all night, and I also don’t want it on them in the heat of the day. Then I let all my drips start around 9am – they can take 2-3 hours to get done, and it doesn’t hurt for them to be watering with the sun up. But that’s just all my personal preferences.
You may also want to move to the flex daily one zone at a time so that you are comfortable with how it’s watering. Or you can be brave like I was — I never did anything but flex daily from the very beginning. It was a big learning curve for me, but oh, what a good learning it was! - Now I keep fixed schedules around just for overseeding in the fall.