Interstellar civilization timekeeping

[Aghanim]

Lets say we have 3 main human colonies in the galaxy:

1. Our own Earth
2. Space station shipyard in the asteroid belt
3. Populated Kepler-442b

Now, they are connected to each other using  wormhole laser communicator, so latency is not an issue, and they have their own atomic clock and can observe the same pulsar, so they can theoretically sync their clocks to millisecond or better, and interstellar travel is relatively cheap. Here is my questions:

1. Space stations in the asteroid belt are not constrained to planet rotation and revolution, so the normal concept of day and year doesn't really exist, hence they can set their own time. Should they follow Earth time, Kepler-442b time, or they can go with their own time? Should they have 24 hour light and working day, or to be friendly to circadian rhythm, have 6 hour day and 6 hour night? Or some other arbitrary day and night hours? How about leap seconds and leap year? Will they still exist?
2. Kepler-442b and Earth have different orbital period and possibly rotation, so they have different year and possibly different time of day. How can they agree on the same day, week and year? Is that even possible?
3. Lets say someone on Kepler-442b want to watch an eSports tournament on Earth through whatever Twitch-like streaming service in that year. How can they convert their local time to another local time on Earth? Currently its just adding or subtracting the time zone offset from UTC, but from question 2 even the length of year and day can change
4. How about interstellar spaceliner ticket departure and arrival time?
5. How about time onboard interstellar spaceliner ticket? If lets say the interstellar spaceliner is transporting tourists from Kepler-442b to Earth should they use Earth time or Kepler-442b time? How about if the interstellar spaceliner have some sort of subspace communicator or any other magic FTL communication device? Should they target Earth as a relay station or Kepler-442b?
6. Can people in Kepler-442b and Earth celebrate Christmas, birthdays or any other annual event together? How about Steam summer/winter sales? How about movie releases, or same-day TV telecast?

[PB666]

First, on the space station there are duty shifts, you have several each day and there are no night cycle. If there were families on board that would be diiferent but then you have a gravity problem. This is just like a hospital with three shifts per day. 

Second, the latency problem spacetime propagates in all directions at the speed of light if you can coomunicate without latency you effectively can see the future, so this can cause paradoxes, not in the setup you describe but slight modifications thereof. 

If we say have earths velocity is relative to a comoving, the speed we expect earth to be moving  if we extrapololated the red shifts we observed to average values. 442 b is relative to a comoving, and relative to that one or the other is undergo more accelerations, this particular world has time dilation relative to the other, and the clocks will tick at different speeds. In this case to communicate, earth would need to send out a timing pulse to identify. The time shift is quite significant because the futher two stars are form each othe the higher the probability and diiferential that the two stars relative motion will be greater than the velocities of close stars. 

[problemecium]

PB666 brings up the same point I was going to. What's going to give us the most grief is the law of Special Relativity. Depending on with what objects we're trying to communicate and how they're moving, we may encounter issues of events being in different chronological orders. On a mild scale, imagine being on a spaceship and getting a New Year's e-card from your grandchildren before getting your Christmas e-card.

Unfortunately this issue is so cerebral and esoteric that we'll most likely not know what to do about it until we actually have an extended space civilization to manage, and until we've invented some form of FTL communication. If we never do, that'll put a big hamper on any interstellar Steam sales.

[magnemoe]

Space station will probably keep some earth time most suitable for them. 
PB666 is right about duty time however lots of activity will have normal business schedule. That is anything who does not benefit a lot from running 24/7. 

The other planet will be in some sort of mess you will have to follow the local day or an variation if its very long, Say an 50 hour day might have an 8 hour siesta. You will follow local year for farming and say summer holidays. Year for religious holidays and events on earth. 

If you have instant communication it will be the same situation as Olympic games on another continent except everything will not be in the middle of night