It’s generally more expensive to depart on a Tuesday, if you have to leave on this day you can still search on Cheapflights to find great options that meet your needs.
Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from Philadelphia to Asuncion as you normally would.
Due to multiple factors, expect to potentially pay more when booking in December. For low rates, June can be a great choice for travel to Asuncion. Flights to Asuncion from Philadelphia in June are about $1,210 on average during June, but can be found for as low as $791.