Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from Okinawa to Mumbai as you normally would.
These are just IATA (International Air Transport Association) codes. They are used in aviation to identify and differentiate airports. That’s why a Okinawa Naha Airport to Mumbai Chhatrapati Shivaji Intl Airport flight would often be abbreviated as a OKA to BOM flight.