In general, when looking for the cheapest flight to Montevideo, try to choose a flight departing in March for the best deal.
From most locations, booking your flights to Montevideo around 60 days prior to your departure date finds the best deals.
From most locations, the cheapest flights to Montevideo are found on a Monday. Booking a Thursday departure is usually the most expensive.
On average you can find the best deals on plane tickets to Montevideo when looking for flights with evening departure times.