@smenard44, sounds like a beautiful yard. Would love to see photos!
Flex Daily configured for warm season grass (St. Augustine) should work well for your lawn as the trees are probably use to frequent, shallow waterings given the previous owner's watering habits. Remember that Flex Daily schedules are all about Just in time watering therefore, it's a timing game for the selected crop. Once the water percolates through the soil and past the root zone for the grass, it'll continue to into the root zone for the trees. Ideally, you might want to consider adding a zone for watering your trees separately -- however if they are part of the lawn as I'm imaging they are, this would be very difficult to do and likely not worth the cost.
Great tip @mckynzee!