How long will items from the Island stay in the island item drop off box?

In order to take items from the Island home you need to transfer them using an item drop off box inside the resort on the Island, and pick them up on the wharf when you return to your village. When doing so the game gives you a warning to "pick up your items as soon as possible." This makes me think that items will vanish if I leave them in the box or too long, or after I perform a specific action (like shutting off the game or visiting the Island again).

Will items vanish from the Island item drop off box, and if so, when?

Solution 1:

As Alissa said, the sign saying "take items as soon as possible" is simply there so you will remember to empty the box. Anything left in the box will just stay there when you return to the island, reducing the number of things you can take home again. It would actually be a way to take things with you to the island had they not disallowed putting things into the pick-up end of the box.

Don't worry, the game gives you plenty of warnings in cases where you might lose items: the island residents always warn you when doing something will sell off items implicitly, anyone sending you mail will remind you to empty your mailbox, because overflow mail is not (never?) received, and the game provides a lost and found (in the police station) for items removed from the ground because there was no room to drop it or because an event or new house is taking place.