It's best to call ahead to make sure they don't have a large group touring that day. We went with a group and bought the tickets ahead. But I'm sure they accommodate walk ins, as long as there's not a huge group already there. Best bet is to call ahead.
Yes, you should have a reservations. I think if you are there at 10:00 and they have room you could join the tour but there is no guarantee they would have room.
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