AU timezones

I’m not happy when I see someone technical quoting a time in summer (eg during daylight savings) which claims to be “AEST”.

It’s almost certainly actually AEDT.

A summary of the abbreviations, which looks reasonably official, is here: Australian timezones.

In summary, AEST, ACST and AWST apply in winter. AEDT, ACST and AWST apply in summer.

The other issue I had with a recent email was it said 12:00pm AEST. I think in this context, they meant midnight AEDT, but it’s confusing. Better to either say Midnight, or use 24-hour time: 00:00.

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5 thoughts on “AU timezones

  1. Terry

    Time for some nitpicking 🙂

    AEST still applies in summer. Only to Queensland though.
    ACDT applies to South Australia and Broken Hill. ACST still applies to NT though.

    So all varieties of timezones operate during the summer.

  2. Philip

    My major beef is people who refer to the mythical “Sydney Time”. There is no such thing.

  3. Jeremy

    EST is still a valid abbreviation for the east coast of Australia. Just because there’s a web page hosted on a gov.au domain it doesn’t mean it’s an officially adopted standard. Interestingly, unix systems refer to both winter and summer time as EST. This is supposed to stand for “Eastern Standard Time”/”Eastern Summer Time”. Though it’s certainly confusing when it’s reduced to an acronym. This particular issue has been the subject of much debate apparently. Still, in speech you’re far more likely to hear “Eastern Standard Time” without the ‘Australian’ suffix.

    So it would seem in this light that the safest bet would be to include the offset from UTC. In some cases it makes more sense to store times completely in UTC and convert to local time when needed. It removes all ambiguity from the times and ensures you don’t have doubled up times recorded when daylight saving finishes. It also makes sense for a web app where you’re expecting an international audience.

    Finally, “Sydney Standard Time” was apparently invented by Microsoft. Somehow completely ignorant of what designation people may actually use.

  4. daniel Post author

    So is there a documented Australian standard for timezones somewhere? Surely there must be.

    Referring to both standard and summer times as EST is pretty silly, don’t you think?

  5. Jeremy

    I’m not aware of any official standard that says we should use say AEST instead of EST. Indeed, if the Americans decided to start calling theirs American Eastern Standard Time (AEST), we’d be back at square one!

    Probably the most relevant international standard is ISO 8601, which specifies how you should share dates and times. Apparently it doesn’t contain any time zone designators. It suggests specifying your offset from UTC when dealing across time zones. Email tends to use abbreviation for US timezones, but offsets for the rest of the world. More a legacy to do with the fact that it was invented there.

    Using the same abbreviation for two different meanings… yes it’s ambiguous though since there are no international standards for timezone abbreviations, probably best to at least quote the UTC offset somewhere.

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