@jerald, welcome to the Rachio community! Thank you for your support.
Sorry for any surprises. Assuming you haven't had any previous watering schedules run on the Iro, your Flex schedule will see the moisture balance as zero for each of the zones on the schedule. As a result, it will run all the zones on the schedule on the first allowed watering day. Once the zones are "topped off", the watering frequency of each zone will trend with your local weather and the water needs of each zone.
Just curious, what vegetation and nozzle setting did you have selected for this zone? To fine tune your zone durations, I'd recommend reviewing this support article, which details this table:
We default start times to 5a. If all of your zones were running, it's possible that this zone was on the last half of the schedule and it's watering time (10:45a) was simply where the zone fell on the schedule in relation to the other zone's watering durations. You can edit the start time of your zone. Please refer to #5 in this support article.
Zone square footage is used to determine water usage only. For details, please see this support article.
Yes, Flex schedules do depend on accurate data to operate. The better the data, the better the results. If you haven't reviewed this FAQ, I'd recommend doing so.
Bamboo roots are thin and fibrous (think big grass roots) and can go down 2-3 feet. The rhizomes, which is the part that actually spreads, usually stay fairly shallow, less than 12 inches. As such, I'd recommend entering a root zone depth of 18 to 24 inches. You can over ride this via your Advanced Zone Settings.
Hope this helps!