I am traveling to Salvador, Brazil, where and when is the best time to buy a plane ticket? Is the flight long?

I am coming from chicago to salvador brazil.

From Poland, Bangkok, London, Rio? A little more specific please.

18 to 20 plus hours. It looks like the round trip is about $1250+ but if you book more than 21 days in advance you can probably beat that price. check out Kayak.com they seem to come up with the best discount prices. Also, when you have found a flight on Kayak, Don't book it! Call the airline direct and tell them the fare that you have been offered on Kayak. Many times they will meet or beat the price. Also ask about specials. you have to ask to get them. Book your tickets on tuesday and try to fly on tuesday, wednesday or thrusday these days are not as crowded so they are usually a little cheaper.