8mm of gap in femur,grafting surgery done from anterior spine on 26.6.14, 8 month old fracture. how much time will it take to heal? estimation please?

Varies: It varies tremendously. It sounds like you have a delayed or nonunion of your femur fracture. Bone grafting (as you had), dynamics ruin, and use of a bone stimulator are all attempts to get this to heal. Make sure you are not using nicotine or NSAIDs, both of which delay healing. Best case scenario- heals in 8-12 weeks, worst case- still does not heal and needs more surgery.