Timezone selection for web apps


Web applications have an unusual problem regarding timezones and formatted, user-viewable dates for a few reasons:

  • several timezones are usually involved, and the determination of which should be used isn’t particularly clear
  • date formatting code for even a modest list of locales isn’t available in browsers by default

Timezones Everywhere

Desktop applications have it pretty simple. Their users work on a host, and that host has a configured timezone. Windows and Mac users have convenient access to those settings in their “System Properties” or “Control Panel”. If a desktop application needs to display the date or create a time, it has access to the local host timezone. Usually there’s no question…this is the correct timezone for an application to use. If a user temporarily relocates to a different timezone, the user is responsible for changing that setting in his system settings.

Web applications have potentially several timezones to juggle as they manipulate time:

  • client timezone
  • server timezone
  • event location timezone
  • site timezone
  • user account timezone

The client timezone is the computer’s system timezone — the timezone set within system properties or the control panel. This timezone is controlled on the local desktop or host environment. JavaScript in a browser has indirect access to this host provided timezone, and that timezone is available as the default — and usually the only — timezone available to a browser-confined application.

The server timezone is the timezone of the physical server on which your application runs. In a global, world-wide application, this server timezone is probably the least relevant of all the timezones because a server can be almost anywhere in the world and is most likely not representative of the user majority.

The event location timezone is the timezone of an actual event; it is the physical event’s location. For example, world cup soccer matches are held in South Africa this year. It might be tempting to use the event’s timezone when publishing soccer match times. Unfortunately, if I’m a Brazilian fan trying to determine a game time, the South African timezone and time display may not be useful and may be confusing. Here’s an example from a Google search page that shows game times for a U.S. English-speaking user:


The site timezone is the timezone associated with the web app’s domain or site. Let’s use world cup soccer again. Yahoo has dedicated sports sites for various locales/regions around the globe. For example, sports.yahoo.com is primarily the U.S. site, but it has navigational links to allow a user to go to other regional versions of the sports.yahoo.com experience. If you look at a similar schedule of existing or upcoming games, you’ll notice that Yahoo chooses to display times using the site’s timezone.

One view of upcoming games looks like this on the U.S. English site. Notice that it uses Eastern Daylight Time for the site’s timezone:


A different look from the Brazilian site shows this. Note that the times use the BRT timezone:

Screen shot 2010-06-23 at 1.09.45 PM.png

The point here is simple: you have lots of choices for displaying time and time zones to your users. Making the choice is difficult. Once you’ve determined which zone to use, the technical issues aren’t nearly as hard to solve.

In this specific blog, I’ll not solve the technical aspects of displaying time in the proper time zone and format, but I will leave you with my personal suggestion. In general, I think a web site should use as much information as it has available to customize information and to present it clearly to its users. For times and dates, it makes sense to me to present that information in the timezone and format that the user is accustomed to seeing. If your site knows that I’m a U.S. English speaker, maybe you should at least display times using a U.S. timezone. Of course, some regions have multiple zones, and that becomes a new problem. However, in the case of the U.S, which has multiple zones, a California resident is probably more likely to know that EDT is a 3 hour offset. It is doubtful that most California residents would know immediately that South African time is …. well …. some other offset. You see, the South African timezone just doesn’t help me much if I intend to actually watch or record the event. EDT is at least a bit more familiar.

There you have it…some ideas about timezones and their display. Use what your site knows about users to display information. The more localized in formats, the better in my opinion.

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