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All Timezones Are Not Created Equal

Novell Cool Solutions: Feature
By Danita Zanre

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Posted: 31 Mar 2005

Have you ever perused the Timezone lookup list for GroupWise? There are over one hundred unique timezones defined in the GroupWise system. And you might ask why considering that there are only 24 hours in a day! Well, of course there are some timezones that are defined by the half-hour, and that accounts for some of the additional zones. That is, of course, not the entire story. What about daylight savings time and how that affects time around the world? What about the same GMT offset (for example GMT +10:00) in both the Northern and Southern Hemisphere? Face it, time is complicated!

Let's look at a few examples of how the wrong timezone can mess up your day!

We don't need no stinkin' daylight savings

There are a number of instances where two different areas that are on the same GMT offset will not have the same daylight savings rules. Let's take GMT -7:00 for example (just cause I live there and like it).

In Colorado, daylight savings time is observed. Arizona is also on GMT -7:00. However most of Arizona does not observe daylight savings (always has to be an exception, right?!?) So on March 12, 2005 when it is 12:00 p.m. in Denver, it is 12:00 p.m. in Phoenix as well. Jump to April 30, 2005. Denver is now on daylight savings time, but Phoenix is not. So at 12:00 in Denver, it's only 11:00 a.m. in Phoenix. Thus, a Phoenix site that chooses the wrong GMT -7:00 timezone setting for GroupWise will suddenly have all of its users' appointments off by an hour.

Upside Down?

Okay -- so it's complicated enough if you live in the same hemisphere as a similar timezone that you've incorrectly identified as yours. What happens if you choose the wrong north/south hemisphere designation? Well, let's take a look. GMT +10:00 is a good one for this! We've got a few. Two in question are "Brisbane, Melbourne, Sydney" and "Vladivostok." Both are GMT +10:00. However, choosing the wrong one will seriously mess up your day!

In the Southern Hemisphere example daylight savings is defined to begin on the last Sunday of October, and end on the first Sunday of March. The Northern Hemisphere example is quite different! Daylight savings is set to begin the last Sunday of March, and end the last Sunday of October. Hmmmm. So, let's look at a couple of days and how this might affect the calendar.

On Saturday, March 12, when it is 1:00 p.m. in Melbourne, it's 12:00 p.m. in Vladivostok. So, it's an hour earlier in Vladivostok -- cool. Easy enough to remember. Let's fast forward a bit though. March 31, 2005, 1:00 p.m. in Melbourne -- what time would you guess it is in Vladivostok? If you say 12:00 p.m. you lose! It's 2:00 p.m.! That's because daylight savings time has switched. How does this happen???

March 12, 2005: Northern Hemisphere is not on daylight savings time 12:00 p.m. Southern Hemisphere is on daylight savings time 1:00 p.m.

March 31, 2005: North -- spring forward 1:00 p.m. South -- fall back 12:00 p.m.

Suddenly the Northern Hemisphere seems to have jumped TWO HOURS. If you have your timezone on the wrong Hemisphere, you will not affect the change by only one hour, you will end up with a two hour mess!

What About the Workstation?

At the system level, you define timezones for the domain and the post office. However, the user's workstation is just as important for setting the timezone for an appointment. GroupWise assumes that all appointments a particular user creates are for the timezone set on the individual workstation. For a particular user this generally will not cause any problems for posted appointments so long as the timezone remains consistent. However, two users sitting across the hall from each other can have problems if one of them has the wrong timezone designation, and sends an appointment to the other. A user in might send an appointment across the hall to a colleague for the summer company picnic. If one of them has a timezone set that observes daylight savings, and the other does not, the appointment will be an hour off.

Moral of the story -- if your calendars seem to be jostling appointments around at daylight savings boundaries, double check your timezone designations!

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