Due to multiple factors, expect to potentially pay more when booking in March. For low rates, May can be a great choice for travel to Guam. Flights to Guam from Colorado in May are about $1,952 on average during May, but can be found for as low as $1,560.
Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from Colorado to Guam as you normally would.