Though Benjamin Franklin suggested the concept of Daylight Saving Time in 1784, it was not implemented in the United States until World War I. Between World Wars I and II, states and communities were allowed to choose whether or not to observe the change. During World War II, Franklin Roosevelt again implemented Daylight Saving Time. Finally, in 1966, Congress passed the Uniform Time Act, which standardized the length of the Daylight Saving Time period. But states and territories can choose not to observe Daylight Saving Time. Arizona, Hawaii, parts of Indiana, Puerto Rico, and some island territories have chosen not to observe Daylight Saving Time.