looking for advice for a dvd based trivia game

I am designing a dvd based triva game for 2 teams, bascially each team would have a buzzer and the dvd would have a few categories that a team could select and then both teams would have to buzz in first to answer the question. I would like to make the game a little more fun without make it too complicated. Each question on the dvd would have a 30 second timer and when the time is out would go to the category selection screen. I think it would be fun to have some sort of challenge opportunity so that if one of the teams say and answer and the other team thinks it is wrong they can say challenge and say another answer. The problem I am having is that the team that buzzes in could just run the time out so that there is never any time for the opposing team to challenge - any ideas on how to create a challenge feature and also have the dvd be automatic so goes to the next question after 30 seconds?