Here's the dilemma: Quizzes have time limits, but PDFs attached in them cannot be annotated on in SpeedGrader. File submissions allow you to annotate in SpeedGrader, but there's no time limit. What would it take to add a time limit to an assignment or the ability to annotate quiz files in SpeedGrader?
(Using available from/until time is a work-around, but we have students all over the world. We don't want students having to submit work at 2 AM because it is due at 10:10 local time.)