Indian Standard Time
The longitudinal extent of India is from 68*EAST longitude and 97*EAST longitude.This amounts roughly to 30*. The 82½*EAST longitude is considered as the standard meridian of India.The local time along this longitude is generally considered as the common time of India.This is known as Indian Standard Time. Indian Standard Time is 5.5 hours (5 hours 30 minutes) ahead of Greenwich Mean Time(GMT+5.5).
For each 1* longitude there is a time difference of 4 minutes.