This is a problem faced by many Indian Solaris Administrators. Even though I also faced same problem. It's very critical when it comes to the exact time computation. Plays a very important role in the security administration too. At the time of installation there isn't any option for setting the time zone to IST, we need to specify the time zone in terms of GMT+(ie. offset from GMT). That too GMT+5.30 Hrs is not possible, we need to either select GMT+5 or GMT+6. The actual problem starts here.
The only way is first install the OS and then do some changes. But even for that to happen our "Indian Standard Time" zone information is not readily available in the “/usr/share/lib/zoneinfo".
So follow the following steps.
1) As a root execute the following command.
#zic /usr/share/lib/zoneinfo/asia (or)
This command (Zone Information Compiler) compiles the zone info present in the file called "asia" and creates a directory called "/usr/share/lib/zoneinfo/Asia" under which there are files which contain the zone info of different Asian zones. "Calcutta" is what we need.
2)Edit /etc/TIMEZONE file and set the TZ variable to "Asia/Calcutta" and reboot the system.
Now if u issue the command date u should b able to see the date in IST.
As root, execute the following: