Update Time/Time Zone settings

One of the easiest way to edit time/timezone on a linux box is to run timeconfig.

$ sudo /usr/sbin/timeconfig

Or if you want to edit stuff manually, make sure /etc/localtime points to the time zone of your choice:

/etc/locatime -> /usr/share/zoneinfo/Asia/Kolkata

This link gives some good information on how to set it up manually :
http://www.linuxsa.org.au/tips/time.html