Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from Dallas/Fort Worth Airport to Cotonou as you normally would.
Due to multiple factors, expect to potentially pay more when booking in July. For low rates, February can be a great choice for travel to Cotonou. Flights to Cotonou from Dallas/Fort Worth Airport in February are about $1,288 on average during February, but can be found for as low as $936.