As much time as you'd like. The audio tour took about an hour. Exploring the rest of the island and getting photos took about another hour. So one could do all there's meant to do in about roughly 2-3 hours including getting travel to and from the island.
There is no limit on how much time you can spend on island. Look for the last boat's departure time. You can stay until then. Remember there is no good allowed on island. You can have water bottle but no other food or drinks while you are touring. Keep that in mind if you are planning to spend more time there.
Go early, you can catch any boat back so you can choose the time you return, all day is good if you like to read everything!
Just pay the fairy
You can stay as long as you want
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