Probably the simplest way would be to set time limits on the quizzes.
But if you have a lot of quizes then I recommend that you use SQL via Mysql admin, which is downloadable from the add-ons page.
To set a timelimit of 10 minutes on all quizes.
SET moodle_quiz UPDATE timelimit = 10
Or for a subset of courses between course id=x and course id=y,
SET moodle_quiz UPDATE timelimit = 10 WHERE course BETWEEN x AND y
Timothy
The time limit still shows on the quiz. Also, the date may have passed to be able to take the quiz, but that doesn't prevent one from taking the quiz at any time.
What's the structure of the mdl_quiz table supposed to be? Maybe in the upgrade, the table structure wasn't changed (if it is indeed supposed to change)