Edit: This bug is fixed since May 4, 2012. Information below is deprecated. We worked on a fix, with the help of Justin to make it as suitable as it could for everybody (git cccef2e).
This is a first step: allowing a real unified time. Next step: allowing a real custom time. But that is another story.
While we thought our viewers shows “SL Time” by default, this is not true everywhere. So be careful when you fix a meeting! When talking to another grid’s member, watch carefully if your viewer gives you a “PST” or a “PDT” time, and ask your correspondent to check too.
Second Live behavior is to use Pacific Time. Which mean PST in autumn and winter, and PDT (one hour more) during spring and winter.
We expect OpenSim to do the same. And there are some believing that this is hard-coded in the viewer, not on the server side.
Both are partially wrong. There is a bug somewhere, and displaying PDT (as it should happen now) depends totally on the time settings of the machine hosting the server. If it’s set on a timezone without time saving, viewer will show PST. If it’s set to a timezone using time savings (like most American and European countries), viewer will show PDT during spring and summer.
As a result, a grid like OSGrid is one hour behind SLTime, and behind all grids having set up their timezone to any European or American city. This could happen if the server is configured in UTC (Coordinated Universal Time, formerly Greenwich time).
And as for now, there is absolutely no way to configure OpenSim to bypass local DST settings.
Hopefully this will be solved one day. In the meantime, look at the 3 letters behind the hours shown in your viewer when you take an appointment or prepare to attend a meeting!
For example, at the time of writing, it is:
12:55 PST in OSgrid
13:55 PDT in Speculoos grid, Second Life and probably a lot of other grids
20:55 UTC in computer souls and a few other places (but Great Britain is observing DST now)