Daylight Saving Time Begins on Sunday, March 8, 2015. Set your clocks ahead one hour before retiring for the night. The main purpose of Daylight Saving Time is to make better use of daylight. We change our clocks during the summer months to move an hour of daylight from the morning to the evening. The rationale behind Daylight Saving Time is to save energy in the summer months by extending the daylight in the evening when more people would be using more lights and electricity.