Due to multiple factors, expect to potentially pay more when booking in December. For low rates, April can be a great choice for travel to Puerto Rico. Flights to Puerto Rico from Managua in April are about $358 on average during April, but can be found for as low as $108.
Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from Managua to Puerto Rico as you normally would.