Celebrating someone's birthday; it would seem rude not to.

FWIW, today I had my attention drawn to possibly the longest (calendar) year ever: 46 BC (708 AUC), the year that Julius Caesar implemented the Julian reform to the calendar. It included a one-off correction to reverse the drift of months through the seasons that had occurred under the previous calendar, as a result of which 46 BC was 445 days long with the new calendar starting properly in 45 BC.

As a result of that reform, the previous approach of an occasional leap month was replaced by an occasional leap day, by doubling 24th February (VI Kal. Mart., hence "bissextus") to a 48-hour day. It was supposed to be inserted "every fourth year", but ambiguity in how that gets expressed in Latin meant that initially the priests actually inserted it every third year (ie "the fourth" counting the previous insertion as "the first"); this continued until 9 BC, and was then corrected by skipping the next three leap days (in 5 BC, 1 BC and 4 AD). Apparently it was not until some time in the 15th century that the leap day was moved to the end of February.