Due to multiple factors, expect to potentially pay more when booking in January. For low rates, November can be a great choice for travel to San Juan. Flights to San Juan from Melbourne in November are about $1,699 on average during November, but can be found for as low as $1,353.
Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from Melbourne to San Juan as you normally would.