How does the equation of time period of a simple pendulum change in a very high gravitational field

I want to calculate the time period of oscillation of a simple pendulum in a planet with a very high gravity. In classical mechanics where time is absolute, the time period of a simple pendulum is $$T=2pisqrt{frac{l}{g}}$$
Where $g$ is the acceleration due to gravity. But in relativistic mechanics, we know that time is not absolute. So how will this change the equation of time period of simple pendulum?