All new sets, as well as other products such as promo cards become legal exactly three weeks after they are released. BREAKThrough will be legal for tournament play on November 25th. The only exception to this rule are cards that are exact reprints of those which are already legal. You can use these cards from the new set before the set's actual release date, since they're just a reprinted version of a card that's already in the format. For example, Float Stone was reprinted in BREAKThrough. Float Stone is already legal in the Expanded format, so if you were to enter an Expanded event before the 25th you would be able to include the BREAKThrough print in your deck.