P.S. Does having more effeciency on the motor mean MORE flight TIME?
All things being equal, it should - your motor will convert more of the battery's power into useful "work", and less into waste heat.
Of course, it depends on whether your motor is drawing exactly the same amps as the "inefficient motor" did. If your replacement is drawing more, you may get the benefit of higher power and thus better flights - not necessarily longer ones!