Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from El Paso to South Pacific as you normally would.
Due to multiple factors, expect to potentially pay more when booking in September. For low rates, October can be a great choice for travel to South Pacific. Flights to South Pacific from El Paso in October are about $1,422 on average during October, but can be found for as low as $778.