Neat. That looks accurate enough to devise some leap year rules. So the tropical year is 668.5921 Mars days long. 665 is 5*7*19, so a Martian year could be 19 months of five weeks of seven days each, with either three or four non-calendar days in a year. Possibly you could group all the non-calendar days at the end of the year for a sort of Saturnalia (hey, it could be a Martian tourist attraction, like Mardi Gras or Carnivale or Income Tax Day. Martians could have parades and bungee jump and hold contests to see how far they could run naked on the surface). .5921 isn't all that attractive of a number--it's close to 3/5 or 45/76. You could I suppose make even years leap years as well as most years ending in 5 (perhaps skipping the leap day in years of the form X5, where ((X mod 76) mod 13) == 0, so 05, 135, 265, 395, etc. would not be leap years).

And start the calendar out with year 0.

Now you need to come up with names for the months (Armstronguary, Aldrinuary, ...).

Do we need a suffix indicating Mars years (akin to AD and BCE for earth)? We have some Latin speakers on the board--AM might be reasonable but it's already taken.