Falsehoods people believe about Australian time zones
There's a whole lot of false assumptions I've heard about time zones in my career, and many times these assumptions manifest in broken systems and broken code, here's an Australian slant on this topic.
Here's a few falsehoods I've seen implemented in systems over my career:
There's 5 distinct time zones in Australia
Often this assumes something diving into groups of states along the lines of WA, NT, SA, QLD, and NSW+VIC+TAS+ACT.
However there's 13 entries in the IANA time zone data base for Australia.
All locations in New South Wales are in the Australian eastern time zone
Broken Hill is located in New South Wales but is in the ACST/ACDT zone (the same as South Australia). This is a throwback to the times where the rail connection was to Adelaide and hence the town and surrounding area took on the railway time. Specifically this area is Yancowinna County
While it's not part of the contiguous New South Wales, Lord Howe island is officially part of New South Wales and they have their own time zone
Australian time zones offsets are multiples of an hour
South Australia and Northern territory are UTC+9:30 minutes in standard time.
All time zone offsets are multiples of an 30 minutes
While it's not a government mandated zone, there's an observed UTC+08:45 zone near the WA/SA border: Australian Central Western Standard Time
If you missed this one the impacts might not be so bad, only 200 or so people live in that area, it's very remote. This includes Border Village
There's a few other +45 minute offsets elsewhere in world too:
- UTC+05:45 in Nepal
- UTC+12:45 in Chatam Islands and +13:45 with DST there (yes the +13 is not a typo).
Western Australia is all on the same time zone
Officially yes, but unofficially there's the Australian Central Western Standard Time zone.
All Australian territory is within 2 hours of offset from everywhere else
At the time of this article being published Lord Howe island is UTC+10:30 and and Western Australia is UTC+08:00.
The best part about timezones is that this could change in the future though!
The time in Northern Territory and South Australia will always be the same
Northern Territory doesn't have daylight savings but South Australia does.
Daylight savings time starts on the same calendar day each year
The usual dates are DST starts on the first Sunday in October and ends on the first Sunday in April. The calendar date will therefore change year by year.
Daylight savings time always starts on the first Sunday in October
For the 2000 Olympics in Sydney DST was started early on the east coast time zones, where it changed on early on 27 August 2000 instead of the usual date.
The clock always shifts 1 hour on a DST transition
At the time of this article Lord Howe island has a 30 minutes DST shift. As far as I know this is the only place in the world that does not shift one hour on daylight savings.
Queensland and Western Australia have never had daylight savings time so we don't need to support them
This one actually came up in the requirements stage of a large project, someone was arguing that I was "overcomplicating" things by wanting to keep track of daylight savings time, since "all our clients for this project are in Queensland and Queensland doesn't have daylight savings time". I guess if Queensland has another referendum on daylight savings time they will be voting NO to keep their systems working!
There was even an officially registered Daylight Savings Party in Queensland, really, no joke.
That project, like many others, will have failure modes if any timezones shift. Hopefully the fallout isn't too bad.
Timezones are hard!
Lots of "simplifying" assumptions turn out to be downright incorrect, and this can be a substantial risk if a requirement is that your timezones need to be exactly correct.
Even if you are only ever dealing with people in your own time zone it's worth having a sensible way of storing dates and times if you ever need to access that information. Even if you are only working on local time politicians can ruin your assumptions in the future. Use UTC to store times and convert only at the boundaries to local times.
The other thing to note is that these complications are just in Australia, one country. If you have to deal with a more international product you'll find there's all sorts of these anomalies all over the place.
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