As the temperature is increased, the time period of a pendulum.

Time period of the pendulum is given by

T = time period of the pendulum

L = length of the pendulum

g = acceleration due to gravity

For Linear expansion:

Where ∆T is the change in temperature

is the coefficient of linear expansion

If the temperature is increased due to the linear expansion, the length of the pendulum will increase which leads to increase in the time period.