A year was a unit of time which typically lasted 365 days, each 24 hours long, across 12 months on Earth. (TV: World War Three, Last of the Time Lords) More specifically, in an Earth-standard Gregorian calendar, a year was 365.25 days long. (PROSE: Instead of You)
A night on Darillium lasted 24 Earth years. (TV: The Husbands of River Song)