Weve always kept careful track of dates. Not as far as stating the exact date every session or anything, but tracking of time is very important. Or main campaign has lasted in real time for 13 years, and in game time for near 80 years, and time is important to us. The date that Twain Ironhelm, Dijin the thief, and the Summoner fought the battle of the Temple of Kovak is an important historical event in the world. The life of the Summoner has shaped the world, and many events in it have become legend and history. When the Summoner put on the Crown of Fire and was twisted by the evil god Firnoch, causing the Mountain of Power to erupt, is a day of sorrow remembered by all. The day Lord Whistlingwind became the paladin king of Ae'rea changed the face of the continent, and later when he was banished by his god Ae'ar and sought sanctuary in the duchy of Falcor, and when Falcor declared independance and became a kingdom decmating an army of paladins trying to invade the forested mountains of the ranger kingdom, are all important game events and game world historical events.
Dates and times are very important to our game and to handwave them would be a disservice to the historicisity(?!) of the world. I couldnt even concieve of not keeping careful record of them.
Its a credit to both the DM and the players of our game that it is so historical and has covered generations. We even ran a variant future game once, set a 1000 years in the future, playing characters that were descended from our original characters, but we didnt know who was descended from who. The DM decided during the course of play who was whos descendant, based upon classes, races, and character personalities. I ended up being descended from none of my original characters because of the personality, arrogance, and magical power of my character, and damn was it a blast.