Time zone settings in Raspberry Pi is hidden deep into the configuration section. In this article we can see how to change the time zone of raspberry pi to IST
1. Open the Raspberry Pi Configuration Settings by navigating to Menu => Preferences => Raspberry Pi Configuration
2. Open the Localisation Tab and click "Set Timezone"
3. Select "Asia" instead of "Indian" or any other option for "Area" dropdown
4. Select "Calcutta" in "Location" option
5. Restart the Pi and now the time zone will be changed to IST on reboot.
Note : You can also perform this change by typing "sudo raspi-config" in the terminal window