I want to know how you to do user time selection, like in forum->user_profile:

('-12', '(GMT -12:00) Eniwetok, Kwajalein'),
.....
('+12', '(GMT +12:00) Auckland, Wellington, Fiji, Kamchatka').

How do they display this, do they hard code this? Two, what do they do to perform Day Light Saving Time?

Thank you.