A week

You keep up the pretense. Walking around naked constantly, watching a lot of porn, rubbing yourself to completion (and complete exhaustion), and slowly reducing your average syllable count when speaking. Spending lots of time with the mirror (which is a turn off... you remind yourself of your sister).

At least for the cameras.

You also take long walks on the beach, and explore the island interior: When there's no cameras, there's no reason to keep up the pretense of idiocy. You still have to come back to base for meals... but can go swimming whenever... and they might have drones or something following from a distance, so you still make sure to touch yourself regularly. No need to talk with no speakers or listeners...

Also, it feels really good when you finger yourself or grab your... well, breasts... the body is really sensitive.

So you spend a week just wandering...