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I would like to know about the time format which is used by Facebook - relative times such as "2 hours ago", rather than absolute times such as "13:35".

Is there any research about which time format is easier to read for humans and why?

time

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    Note how you can tell on the right which article came first, while on the left you can not. There can be situations where this is important. – PlasmaHH Sep 19 '17 at 11:47
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    Just in case someone decides, on their app, to add a fuller date, please, please, please : use the international iso8601 standard : In full: YYYY-MM-DDThh:mm:ss+hh:mm (ex: 2017-11-12T21:12:01+05:00, if you need timezone too). Please don't invent 'yet another date format' with all their ambiguity and "non-standard"-ness. There are shortened versions as well (see the link). Keep the ':' between times, please (the 'T' is really usefull in logs, and arguably less so in a human context, but I'd still keep it to get it to be more known and used globally). – Olivier Dulac Sep 19 '17 at 13:23
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    My personal experience is that I have difficulties with relative times. I find myself calculating the absolute time in my head, which might not be as easy as it should (e.g. when it says "17 hours ago" and I read it in the morning). If you use them, please provide a setting to use absolute times instead. – Scz Sep 19 '17 at 14:08
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    Just please allow for some way to obtain the actual time a document was posted/generated. Even if you have to hover for alt text or tap to toggle between the formats, it is always so frustrating to see a bunch of documents with the same relative time and no way to discern reading order. – zero298 Sep 19 '17 at 15:29
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    @OlivierDulac Agreed with Mr Lister; at minimum, for human-readability, replace T with a space and add a space before +. The gaps create a legible-at-able-glance group of 3 things: Date, Time, Timezone. The ISO standard is one big blob that takes a moment to understand. – Izkata Sep 19 '17 at 18:19
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You could also show both formats: 13:35 (2 hours ago)
This way the user could figure out either one easily, depending on what they wanted. You could also allow searching/filtering by either.

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    Similar to this, StackExchange shows the absolute time on hover – Izkata Sep 19 '17 at 18:33
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    I didn't know that, thanks for the notice, @Izkata – Clément Sep 19 '17 at 20:13
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    Didn't notice it either. Wouldn't recommend it as a solution if users never notice it. – ESR Sep 20 '17 at 4:56
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    @Izkata this seems to be a widely-supported feature. Another example is GitHub, and I'm sure to have seen this on many other sites. – Ruslan Sep 20 '17 at 7:12
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    @EdmundReed perhaps you never felt the need to know the exact time of a post. I've wanted to know which was two answer was first a number of times, and hovering over the rough-relative information seemed quite an obvious first attempt. OTOH, it never gets in the way when you don't need the exact time info (which is very common). So I'd say, a hover-tooltip is an excellent solution. – leftaroundabout Sep 20 '17 at 11:41
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I'm not sure about hard research, but there's a good article from UX Movement:

Absolute vs. Relative Timestamps

When to use absolute timestamps:

There are times when users need to look back on past content to retrieve information. Without absolute timestamps, users can’t target a specific period to find the information.

Sites that host photos, documents, messages, tasks and events all need absolute timestamps. These content will hold utility in the future when users need to reference them. Use absolute timestamps when users can go back and make use of past content.

When to use relative timestamps:

Accuracy isn’t important with relative timestamps, but immediacy is. When users want to know how long ago a site published a post, they prefer time units in written form. This way they don’t have to mentally calculate dates and times and count back from the present day.

Not only that, but users don’t have to convert time zones with relative timestamps. Content published an hour ago or five hours ago makes no difference to users who only need a general sense of recency.

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    "If your site content updates often, or has a lot of user activity, you should use relative timestamps. Sites that publish news, or have forums where users post links and comments need to show immediacy. This allows users to stay up-to-date with new information as it comes in." Is this widely accepted? Especially with news on ongoing events, I'd like to be able to relate the timestamp of the news by minute to the event and other news sources, I don't see how I could even do that with relative timestamps. – JiK Sep 21 '17 at 11:25
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    This is the only answer that actually addresses the question of 'is there any research'. – Möoz Sep 21 '17 at 23:31
  • Pity the author of that article doesn't cite his sources or studies. It just reads like an opinion piece. – Roddy of the Frozen Peas Sep 25 '17 at 5:50
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When you use absolute timestamps, you need to find out which timezone the user is in. This can be a guess based on IP address (which may be wrong) or a setting in the user profile (which needs to be filled out during user signup, adding another field), or a mix between both.

It is confusing to the user when you get it wrong. When I travel abroad, some websites show timestamps in my home timezone and others use the one where I currently am. The daylight savings switch in autumn will also show timestamps between 2AM and 3AM seemingly out of order, or imply that only a few minutes passed between two entries, when it was really an hour.

StackOverflow shows relative time for recent posts and switches to absolute (date only) after some time, when no one cares about the time of day a post was made anymore. What is best for your website depends on your application, whether there will be access to old material, whether users need to follow nonlinear reply chains, ...

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    Or just give the timestamp in UTC, and let the user decide if they want to use a TZ offset or not. – Monty Harder Sep 19 '17 at 15:47
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    @MontyHarder, that is okay for people living in the UK about half the time. Specifically, the half that is in winter. – Simon Richter Sep 21 '17 at 9:38
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    If you format it in the browser, that browser usually knows the time zone of the computer (which often is the same as the user's one). – Paŭlo Ebermann Sep 23 '17 at 23:35
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    @MontyHarder Go out on the street, grab the first 10 people you find and ask them in which timezone they are. I'd be surprised if you got more than 60-70% correct answers (and that's probably overly optimistic). – Voo Sep 24 '17 at 14:58
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    @MontyHarder UTC seems to be hard for many people. Again and again I encounter people/websites who think UTC is "the time in the UK". Which of course it is only when DST isn't in effect (less than half a year). – Abigail Sep 24 '17 at 22:50
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The choice between absolute (13:35) and relative (2 hours ago) is made depending on the type of content you're browsing. Absolute timestamps are used when your user needs to reference something; sites that host photos, documents, messages, tasks and events all need absolute timestamps. You need to know the exact date something was published, it's not important to know how long ago that was from where you are now.

Relative timestamps are more emotion oriented; when your site content updates often, or has a lot of user activity, you use relative timestamps. This is important because you are trying to see whether or not something is new compared to where you are now. A stamp saying 2 hours ago is much faster at telling you this is fresh content. You don't have to mentally calculate dates and times and count back from the current time. This also avoids the whole timezone issue.

Source: http://uxmovement.com/content/absolute-vs-relative-timestamps-when-to-use-which/

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