If you want to post the time for an event or something, there are two options. It could be in Egypt time (which would be appropriate for a mushroom collecting party, for example) or real world time. Usually, it'll be real world time.
But which time zone? It should always* be UTC/GMT (UTC and GMT have slight technical differences, but you can use them interchangeably).
Note: If you're certain that everyone involved knows the same timezone, it's an option. But it's rare that you can be certain this is true. The exception is when you're discussing a real world event, such as a meet-up. Then using local time makes sense.
It's also preferable to use the international date format, YYYY-MM-DD.
This way, you have a much better chance of everyone getting the time right.
Okay, so UTC... Why? Well, let's look at an example.
12:00 CST.
When is this?
Well, if we look at http://www.timeanddate.com/library/abbreviations/timezones/ we see there are 3 CSTs (but lets ignore the Australian summer one. Because I live in the Australian CST, and we use CDT for daylight savings time).
So either Australian central time, or North American central time. Which is it?
Well, right now, North America is in summer. So they're not using CST at the moment (unless there are states/etc that don't do daylight savings. But that's another problem). So it's probably the Australian one.
On the other hand, without wanting to be stereotypical, it's my experience that when people online assume that their local view of life is shared by everyone else (local timezones, sporting events, whatever), it's usually someone from the USA. This may simply be because there are many people from the USA online; and I'm not saying that everyone from the USA is like that (I know of a lot of Americans who are quite aware of the wider world), just that this is what I have observed.
So even though, until the southern hemisphere gets into summer, CST is only (see above note) in use in Australia (unless there are other CSTs not listed on the above website), and hence, CST currently means the Australian version, if we see it online, there's a fair chance that, not only is the intention the American one, the poster also meant North American CDT.
Clear as mud?
Okay, lets revisit the other big issue. Daylight savings time. It's not universal; the entire northern/southern hemisphere doesn't change their clocks by the same amount at the same local-time on the same days each year. Some places will change sooner or later than others, and some won't change at all.
For example, in Australia, Queensland is on the eastern coast, so uses (Australian) EST. This is UTC+10:00. In South Australia, we're on (Australian) CST, which is UTC+09:30. However, Queensland doesn't do the daylight savings thing (being close to the equator). So in summer, SA becomes a half hour ahead of QLD. Who, outside of Australia, can be expected to know this? Not many people have any reason to know.
Everyone should know their own UTC offset, in winter and in summer (if you don't, it's not hard to find out. That website above, for example, will tell you). UTC also does not get adjusted for daylight savings (although this can be a trap for people who confuse British time with UTC), so you don't have to worry about that.
If you see a time in UTC, then you only need to apply one offset (and you only need to know one or two offsets (depending on if daylight savings time is used where you live)). It's much simpler, and you can be sure that if both the reader and the writer apply their offsets (which they should both know) correctly, they will have the correct time.
You don't always have to do it yourself, though. The ingame calendar and the wiki both support adjustment for you. Ingame, you only need to set your UTC offset (Self->Utility->Set my Time Zone), and on the wiki, you can put braces around the time, eg { 2008/08/10 14:30 UTC } without the extra spaces gives:
And please use that date format (correctly, it should be YYYY-MM-DD, but the wiki seems to insist on using a slash. For the automated dates on the wiki, use the slash, anywhere else, use dashes. But as long as you use the 4-digit year first, it will be unambiguous).
Lets have another example. 3/1/08. We know it's not the international format (YYYY-MM-DD, which, by the way, is the same order as we use for time, largest first: HH:MM:SS). But is it day first (third of January, as used by most of the world that's not using the international format) or month first (first of March).
Well, this one is even worse, because you don't have a marker like CST to warn you that it's not exactly the same as what you use. Chances are, when you saw the "3/1/08", you interpreted it using whichever order you'd normally use, without even needing to think about it (afterall, we deal with time and dates so often, it becomes natural).
If the date is greater than 12, or the same (numerically) as the month, then it may not be a problem that time, but for more than a third of the possible dates it's ambiguous. (12 times a year, the day and month are the same. Any date above 12 is okay. So 11 ambiguous dates per month, 11*12=132/365 days (ignoring leap years) = 36%).
It's not too hard to write in the international format, just takes a bit of effort at first to remember. After a short time, it comes naturally.