I read your source and can't figure out how they came to that equation. When I do the math out of \frac{I}{Mgh} and substitute \frac {ML^2}{3}for I, I get 2\pi\sqrt{\frac {L}{3g}}instead of 2\pi\sqrt{\frac{2L}{3g}} Where did the 2 come from in the numerator in the correct equation?
EDIT...