I’d start with 1ft square (for canopy coverage) for a saplings as your “coverage” area to calculate in/hr. Increase that at least once a year as your saplings grow — I measure the radius from the trunk to the drip line and calculate the area. I personally set Iro in Flex Daily to a single tree instead of averaging it across the zone. See this thread and included spreadsheet on how to calculate inches per hour — since these are saplings you may consider reducing the root depth a bit and deepen it as they grow. However for my orchard, I do water to 24” depth for new trees just to keep things simple and encourage deep root growth.
With 2 GPH emitters, 1ft2 canopy that you‘re targeting watering for, it should come out to ~1in/hr but please don‘t take my word for it — definitely understand how the spreadsheet and conversion formula works.
Another resource for Flex Daily: