Question

Perhaps this question should be broken up into two posts, but I currently have an API for a few business customers. I am currently using ISO 8601 timestamps with a UTC time zone to represent times. However, I don’t like the idea of these timestamps being attached to any timezone because the times should be the same no matter what timezone you are in. 5PM UTC should be 5PM CST, etc…

I know that you can leave the Z off of an ISO timestamp, and it will be interpreted as whatever local time you are in. Is this ok practice? And if so, how do I do this in Ruby? I read the doc for the Time class and didn’t see anything about this.

EDIT: Let me re-word this just a little bit, or atleast clarify something. The reason why I’m seeking timestamps that aren’t attached to a timezone is exactly because I know that my client servers and API server will hardly ever match up. If a client is submitting an event with a time, that time needs to be ambiguously equal to the ambiguous locale specific to the event that the user is working on.

That’s a mouthful…assume that I’m working on an event scheduler. Each event belongs to a storefront or location of a company. When times are being shown for a location, it is assumed that the times shown are in the timezone of the location, and for clarity’s sake should never be shown at a time formatted to a user’s local timezone. If I’m looking at the scheduler on the East Coast, but looking at events for locations on the West Coast, the times I should see should be local to the locations on the West Coast, not adjusted for my timezone.

I know a solution could be to simply store times with timezone information for the location its associated to. But the use case that a user would want to convert a time to their timezone is VERY rare, and I’d rather make implementing my API easier…this was actually my original implementation but implementing the API in many different environments and across multiple programming languages, it became clear that it is a hurdle to show times local to that timestamp’s timezone for a lot of languages. If a user wanted to convert times to their local timezone I could easily store global timezone information for the location object itself.

Answer 1

I don’t know what you mean by “the times should be the same no matter what timezone you are in. 5PM UTC should be 5PM CST, etc..”. 5PM UTC clearly isn’t 5PM CST!

Anyway, I don’t think that what you are proposing is an ok practice. Suppose you leave off the Z and have a timestamp be interpreted as whatever local time you are in. Since this is a network API, the client and server might not be in the same timezone. When the client submits a “local” time, what does it mean? The local time on the client (if so, how does the server know what that is?)? The local time on the server? It’s ambiguous. This is the crux of the reason why just about the only reasonable thing to do is to use UTC throughout.

What you can do is attach a timezone to a timestamp if it might be relevant. For example, “you should observe one minute of silence at 2012-11-10T22:00:00Z in honour of the soldiers who died in WW1” sounds weird because Rememberance Day isn’t on November 10! “you should observe one minute of silence at 2012-11-11T11:00:00+13:00” sounds a lot better once you put that New Zealand time zone in there… In this case you can keep and timestamp (in either local or UTC) together with the timezone offset (e.g. store both of them together in your database).

It does, however, depend on what your times represent. For example, in “at equinoxes, sunset happens at 18:00” it makes sense to use an abstract time that isn’t qualified with a timezone (it’s true in every timezone, and/or you’re talking about solar time). But attaching a date to this abstract time makes little sense, so I don’t think you would be talking about ISO8601 in this case.