Demand for a separate TimeZone for North East India is not new and it appears during 21-23 June in every year when it becomes the longest day in North hemisphere. During summer, the sun rises in North East India at 4:15AM and the sun sets around 6:15PM. During winters, the Sun rises at around 6:15AM and sets at around 4:15PM, all in IST ( Indian Standard Time).
If one sees the map of India, North East India lies further to the east of Nepal and Bhutan, but Nepal has time 15 min ahead of IST while Bhutan has time 30mins ahead of IST. But North East India follows IST, and is behind Bhutan and Nepal time.
Tea Estates in Assam used to folow their own Tea-Estate time, though they are also now a days adopting IST. Many Tea Estates starts their office at 6AM in Assam.
Most of the people in North East India get up at 3:30AM during summer, so they have to sleep by 8PM in the evening. While at 8PM, most of the western part of India are not properly dark yet. During winters, the Sun sets by 4:15PM while it rises by 6:00AM.
Many people from North East India living in Western Part of India have to communicate with their family and relatives accordingly.
Most probably, it makes sens to have a separate TimeZone for North East India in order save daylight. There could be some logistical issues like train timing and others, but with increasing literacy rates and usage of smartphones, following two timezones in same country, India, should not be a logistical nightmare anymore.