The truth is more ridiculous, in that every year it does it wrong by about 8 hours, so they need to tack on an extra day every four years. Except it's
not quite 365.25 hours, so you skip the extra day every year that ends in "00". Except that's
still not quite right, so every
four hundred years you skip skipping the extra day (hence, 1900 was not a leap year, but 2000 was). Except that's
still not quite right, so every couple of years at seemingly random when it seems necessary we add a
leap second (the last few times it happened were in 1998, 2005, 2008, 2012, 2015, and then again in 2016, but we've done in 27 times since 1972, when we did it
twice that year) on either June 30th or December 31st.