Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from Oakland, California to Samoa as you normally would.
Due to multiple factors, expect to potentially pay more when booking in September. For low rates, April can be a great choice for travel to Samoa. Flights to Samoa from Oakland, California in April are about $1,411 on average during April, but can be found for as low as $904.