Just a brief thought... why are we stuck with days, months, weeks, etc... Space is deep and wide with enormous amounts of possibilities.

So why do not we go with 100,000 seconds as a "day" (86400 currently on Earth), 1 Msec for a "week", 5 Msec for a "month", 50 Msec for a "year"? Just give these checkpoints different names :)

Keelah se'lai!

@Dirk: and if we have, for example, bases on Mars and Venus in addition? I would definitely prefer something... universal and not depending on any place.

Here are my suggestions which are from my platform:

• Time 
• 
  
  • * not adjusted for Daylight Savings (which needs to be abolished)
  • * Asgardian Standard Time Zone (ASTZ) - select +0:00 GMT as our time zone
  • * Asgardian Standard Time (AST) - 24 hour time clock for based on AST
  • * Asgardian Interstellar Time (AIT) - use a decimal time as standard. This may be useful as different planets have different terrestrial clocks and calendars. This will also provide something that is uniquely Asgardian and can be used to to schedule meetings across multiple time zones without the confusion of 12/24 hour clocks and time zones.
• 
  
• I have code written in javascript and PHP which can do the decimal time conversion.
  This works well with our amazing calendar.

@James: back again - why are several time counts necessary? One and universal saves resources on many levels.

@Alexander, multiple time counts are needed for people living within certain places. A way to measure time locally to keep track of the day, for example. The universe doesn't have a universal reference frame, so we have to create one that's useful to us.
I believe we should abolish timezones, and use the Prime-Meridian (a standard meridian agreed on by most of the world) as a reference, and measure the angle of this meridian to the sun, with 180° being (approximately) solar noon, and 0° being when the meridian is facing the opposite direction of the Sun. Using this notation, 1 degree would be about 4 minutes, and more precise time can be represented with arcminutes (1/60 a degree, or 4 seconds) and arcseconds (1/60 an arcminute, or 1/15 a second).

That said, that would be an ideal system and would require calibrating systems to the prime-meridian, instead of just using the built-in timestamps computer have.
For convenience, using GMT time (or what James is calling AST) should be fine, in my honest opinion. For non-Earth localities, using a degree system might not be such a bad idea. The only other frame of reference I think we can use would be out position within the galaxy, but that's too large to be useful to humans (which is for whom Asgardia exists).

In my opinion though, the adopted calendar is kinda silly. It doesn't achieve anything beyond keeping a whole number of weeks in each month. Weeks aren't even an important enough concept to care if they spill into multiple months. I'm expecting drastic calendar drift to occur with the extra 13th month.

@Jeremia: time is universal by itself (well, still relative, but let's keep this out for the moment), more to say, the humankind has to become a space nation (species, whatever) - not bound to any specific location :)

Even a space-nation for humans will have to make use of local times that are useful to humans. Humans have evolved on Earth, and so our sleep-cycles are bound to Earth's days.

@Jeremia: so, do you imply that humans are unable to live anywhere except Earth? :)

The calendar is amazing.
I have been advocating this calendar for quite a few years.
That advantage simplifies scheduling and removes unneeded cognitive load from scheduling.