The notion that extended Daylight Saving Time by several weeks was based in energy savings, but in fact, while lights may have burned fewer hours, there was more gas and electricity expended as a result. DST now starts three weeks earlier and ends one week later.
On a related subject. We know that one day is equal to one rotation of the earth, which is divided into approximately 24 hours. Time is either added or subtracted to or from the atomic clock to make period corrections due to the inaccuracy of that time standard.
What about the year? Are there precisely 365.25 days in one spin around the sun? I doubt it. How long does it take to notice that the sun is not in the same position on January 1 of every year? Are there periodic corrections make in this measurement? I don't know!
