The local times of places which lie on different meridians are bound to differ. The sun rises two hours earlier in Arunachal Pradesh as compared to Gujarat in the west. This causes a time lag of two hours from Gujarat to Arunachal Pradesh. To avoid confusion due to time differences and to have a standard time for reference, the time along the meridian (82° 30' E) passing through Mirzapur (Uttar Pradesh) has been taken as the standard time for the entire country. This is why the watches show the same time.
Arunachal Pradesh lies East when compared to West.
Mediterians decides the time of a particular place. The main mediterians pass through Arunachal Pradesh is 96 degrees. In Gujarat the main mediterian is 70 degrees. Because of difference in degrees sun rise early in arunachal Pradesh when compared to Gujarat. Time will also be different. But they follow IST which is +5 hours 30 minutes different than GMT