If you see the current trains running from BZA - RJY via GDV, BVRT are taking atleast 3 hrs 45 mins. The fastest being Cocanada AC SF. If you give highest priority to your IMG also, it needs 3 hrs 30 mins. Overall with your logic 6 hrs 30 mins is required. If you want your IMG to go via BBS, then why can't it change at RJY ? It will save fuel like Visakha exp.