How do Social Networking applications convert server time according to viewer's timezone

Question

How to convert the UTC time according to viewer's timezone?

I heard that it's not possible to get the timezone of the viewer, but then how do social networking services like FB, twitter do this ?

Edit: I have registered users on my application.

[Already there](http://stackoverflow.com/questions/338482/can-you-determine-timezone-from-request-variables) — sudmong, Jul 22 '11 at 07:00
Social networking sites usually ask their customers about their location for their profiles; so later calculating their local time is trivial. — SJuan76, Jul 22 '11 at 07:04
@SJuan76: but users do travel internationally and they dont need to tell their timezone each time they login from some non-native timezone — Rajat Gupta, Jul 22 '11 at 07:10
Use the machine local timezone. Anyway do not overwork, it is a website not a clock so if the time is not set to someone's standar is not that important. It is more important that items are kept in order than the actual time. — SJuan76, Jul 22 '11 at 07:29

score 0 · Accepted Answer · answered Jul 22 '11 at 06:52

0

It is possible to get the user timezone, but this is done with javascript (get the detect_timezone.js). You most likely do that when users are registered.
Another, worse way is to approximate the timezone based on the IP
and finally (with combination of any of the above), you can give the user a choice to select his timezone in his settings

answered Jul 22 '11 at 06:52

Bozho

Or use the system time of the client machine (via JS) and just hope that it is correctly set (almost all of time it is). – SJuan76 Jul 22 '11 at 07:03
that js library checks that as well – Bozho Jul 22 '11 at 07:21

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