How does Diver movement work in forbidden island?
You got it right the first time. In your example, it takes the diver 1 move action to go from T1 to T2. The Diver is incredibly useful for quickly getting around the island while it's flooded. It's not as overpowered as it would initially seem... until tiles start sinking, the Diver hasn't any other special abilities. In later stages of the game, you can ensure he'll probably survive.