There have been some requests for a timed question as opposed to an overall timer on the entire assignment. Below you will find a question that can be used to provide a countdown timer on individual questions, that forces students to move onto the next question when the timer runs out. The question contains a script that simulates the student pushing the next button after a defined amount of time. In order to effectively utilize a timed question an instructor should disable the assignment option for "allow resubmit" (otherwise having a timed question is completely pointless, as the student could simply return to the question later).
Here is what the question and timer looks like:
Here is a link to the question, for you to import: link
I forgot to mention, for you to see it work the question must be on an actual assignment. Also it goes without saying that the assignment will need more than one question.