Period of Pendulum

A pendulum that vibrates can be classified as ‘simple pendulum’ and ‘physical pendulum’. A simple pendulum is a case in which the angular motion of an object can be ignored, such as a small object suspended from a string that can ignore mass. In fact, most pendulums are a ‘physical pendulum’ instead of a ‘simple pendulum’.

Since the experiment of Galileo, We think that the amplitude and the cycle of the pendulum are not related. This only applies if the amplitude of the pendulum is very small.
In practice, the pendulum cycle increases as the amplitude increases.