Due to multiple factors, expect to potentially pay more when booking in May. For low rates, October can be a great choice for travel to Guam. Flights to Guam from New York in October are about $2,023 on average during October, but can be found for as low as $1,844.
Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from New York to Guam as you normally would.