Damn Romans

How many hours would you have to wait if its 11am and your meeting is at 12am ?

Source http://naggum.no/lugm-time.html

The Roman tradition of using Ante Meridiem and Post Meridiem to refer to the two halves have survived into English, despite the departure from the custom of changing the day of the month at noon. The Meridiem therefore has a very different role in modern usage than in ancient usage. This legacy notation also carries a number system that is fairly unusual. As seen from members of the 24-hour world, the order 12,1,2,...11,12,1,2,...,11 as mapped onto 0,1,2...,23 is not only confusing, it is nearly impossible to make people believe that 13 hours have elapsed from 11 AM to 12 AM. For instance, several Scandinavian restaurants are open only 1 hour a day to tourists from the world of the 12-hour clock, but open 13 hours a day to natives of the world of the 24-hour clock.
The Roman tradition of starting the year in the month of March has also been lost. Most agrarian societies were far more interested in the onset of spring than in the winter solstice, even though various deities were naturally celebrated when the sun returned Most calendars were designed by people who made no particular effort to be general or accurate outside their own lifetime or needs, but Julius Cæsar decided to move the Roman calendar back two months, and thus it came to be known as the Julian calendar. This means that month number 7, 8, 9, and 10 suddenly came in as number 9, 10, 11, and 12, but kept their names: September, October, November, December. This is of interest mostly to those who remember their Latin but far more important was the decision to retain the leap day in February. In the old calendar, the leap day was added at the end of the year, as makes perfect sense, when the month was already short, but now it is squeezed into the middle of the first quarter, complicating all sorts of calculations, and affecting how much people work. In the old days, the leap day was used as an extra day for the various fertility festivities. You would just have to be a cæsar to find this unappealing.

The Gregorian calendar improved on the quadrennial leap years in the Julian calendar by making only every fourth centennial a leap year, but the decision was unexpectedly wise for a calendar decision. It still is not accurate, so in a few thousand years, they may have to insert an extra leap day the way we introduce leap seconds now, but the simplicity of the scheme is quite amazing: a 400-year cycle not only starts 2000-03-01 (as it did 1600-03-01), it contains an even number of weeks: 20,871. This means that we can make do with a single 400-year calculation for all time within the Gregorian calendar with respect to days of week, leap days, etc. Pope Gregory XIII may well have given a similar paper to this one to another unsuspecting audience that probably also failed to appreciate the elegance of his solution., and 400 more years will pass before it is truly appreciated.

Other than the unexpected elegance of the Gregorian calendar, the world is now quite fortunate to have reached consensus on its calendars. Other calendars are still used, but we now have a global reference calendar with complete convertibility. This is great news for computers. It is almost as great news as the complete intercurrency convertibility that the monetary markets achieved only as late as 1992. Before that time, you could wind up with a different amount of money depending on which currencies you traded obscure currencies like the ruble through. The same applied to calendars: not infrequently, you could wind up on different dates according as you converted between calendar systems, similar to the problem of adding a year to February 29 any year and then subtracting a year.

If you said one your wrong.