September is a wonderful time to go, more mild temperatures and the crowds are just starting to thin. With one day you could do a lot, but it mostly depends on which hikes you choose and so forth. Observation point could take most of the day by itself, and even a small portion of the Narrows/Riverside walk will take up a lot. I recommend starting really early and planning ahead. If you leave something undone you get to come back!
September is great, one full day is enough, park is open 24h, take a good water shoes and a stick to walk the river for an hour or so, it's to far to walk to the canyon without proper gear.do walk/ hike from #5 to #6 ,easier that way.
Yes, one day is more than enough time for the major hikes.
Yes it is, and it depends on what you have plan if you are gona do the trails it won't be enough time.
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