I decided to let my students take the exam home to complete it. I finished writing it earlier this evening, and they'll have more than a week before they have to turn it in - but they're also finishing term papers due on Thursday, so I suspect most of them will wait a few days before starting the exam. It's already posted online, so they can start when ready. They were all very excited by the change to a take-home exam, and I'm hoping that, with less pressure and more time, they'll all do very well.
Because honestly, all of my "mean teacher" talk aside, I want my students to do well. It makes me sad when I have to flunk plagiarists and assign low grades to students who haven't done all the work. I would rather read good papers and tests.