Before the 1500s, leap years was solved by simply having a second 24 February. From the 1500s to the 1700s, the concept of 29 February was introduced.<p>Imagine having to build a time management system or calendar handling, that needs to support having two 24 February in a row. The year has the same amount of days - officially - as any other year, just one day that has 48 hours.<p>Happy leap day!<p>(As for why it was the 24th, well, the short answer - as always - is the Romans.)