It apparently shows the time when the island sinks under the water.
What time is it showing?
Hint 1
Try to imagine what the island looked like when is sank into the sea.
What would happen to the monument?
Hint 2
The inscription on the monument is the time
Hint 3
The inscription on the monument is only the top half.
Super Hint
How would the inscription on the monument look if it was reflected in the water?
Answer for 'Island Mystery'
The answer is '8:30'.