Which statement best defines a universal law

a. it is in fact some of the time

b. it is in effect at all times

c. it changes over time

d. it operates only under specific times

B. It is in effect at all times.

Explanation:
By definition, a universal law is immutable, meaning that it does not change and it is in effect at all times. 

This definition should be appled within the scope of what "universal" means.
For example, the law of "Cause and Effect" is stated in physics by Newton's third law: To every action, there is an equal and opposite reaction.  

Discussion:
Our perception of the universe is limited usually to our solar system, within a physical and material universe. We cannot be certain that our accepted universal laws apply in the same manner in a nonmaterial or spiritual universe.

The term universal law is mostly used in law and ethics and describes law or principle that is universal acceptable, applicable and translated. The universal law is the most legitimate law.
According this explanation, the following statement best defines a universal law:
B. It is in effect at all time.