Let us say you need to display time for different zones or cities. Sure you can use The World Clock - Time Zones located here. If you need a different time zone at a shell prompt or script use old good date command.
Different timezones can be displayed by changing the TZ environment variable.
TZ Specifies the timezone, unless overridden by command line parameters. If neither is specified, the setting from /etc/localtime is used by Linux/UNIX computer.
Display current date and timezone
Tue Jul 24 22:05:54 CDT 2007
Display time of different timezones using the date command and TZ variable
Set timezone to PDT:
$ export TZ=America/Los_Angeles
Tue Jul 24 20:12:01 PDT 2007
Or set timezone to IST:
$ export TZ=Asia/Calcutta
Wed Jul 25 08:46:12 IST 2007
Remove the TZ variable with unset command:
$ unset TZ
Tue Jul 24 22:17:31 CDT 2007
Read date,bash,unset command man page for more information. Hope this small tip will save your time and see a different time zone.