It (Shampoodle that is) must first be unlocked by spending at least 10,000 Bells between the Able Sisters store or Kicks. Kicks must also be open for at least 7 days before construction begins. It takes 4 days for Shampoodle to be built.
When the player has upgraded from the tent to the house, and then upgraded once after that, Isabelle will introduce Tortimer the next day when the Player starts the game. He will ask the player to meet him by the dock. Once at the dock, Tortimer will tell the player about the island. However, it is not until the next day that Kapp'n will appear with his new motorized boat at the dock, which will be ready to take the player to the island for a fee of 1,000 Bells per round-trip.
Two house upgrades will get the ball rolling. At that point, you just need to talk to Tortimer at the dock, and you can go the next day.
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