Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from Mumbai to Nantes as you normally would.
Related info for your journey
Useful info, stats and facts about Mumbai to Nantes flights.
These are just IATA (International Air Transport Association) codes. They are used in aviation to identify and differentiate airports. That’s why a Mumbai Chhatrapati Shivaji Intl Airport to Nantes Atlantique Airport flight would often be abbreviated as a BOM to NTE flight.