What should I consider when deciding whether to delay an exam?

Exam dates announced at the beginning of the semester should only be changed with a highly compelling reason. The syllabus of a course is a contract with the students. Even if 90% of your students prefer the delay, if one of your students has to cancel an airplane ticket for a conference visit or miss a wedding, a balance has not been struck.

If I were a student in which an instructor tried to change an exam date as late as "the day before", I would certainly lodge formal complaints with the department and the institution. Please do not do this.

In your initial post, you'd not given any reason to believe that you couldn't simply move a bit of material to the next exam. That is by far the better option.

If for some reason delaying the exam is truly unavoidable, you should feel obligated to offer make-up exam times for students who may be unable to attend.

Yes, consider all of those things. But note that you will disrupt some of the students while advantaging others. The ones most likely to be disrupted are the best students with a regular schedule.

But another alternative is to change the exam so that you don't "cover" as much material and let that flow into the next exam. To me, this is a far better practice.

There is a problem with learning that unless we use certain practices to firm up our understanding (repetition and feedback, which I write about here quite often) then we are most likely to recall the thing we looked at last and it can interfere with recall of things learned earlier.

Actually, I think that a good practice is to avoid including material from the just previous lecture on any exam. Or at least, avoid covering it in such a way that requires deep understanding.

From a student's perspective, I would expect the following three things if you were trying to reschedule an exam:

• At least an attempt to bring it up with the class and poll, talk about it. Who knows, maybe your new date conflicts with another class everyone is taking and they'd rather not move it.

• At least a week's notice, probably more.

• Finally, flexibility for anyone who can't take the new date. People set work schedules, travel, etc. If you change an exam, I would really expect you to let me take it at another time. On the other hand, if you've made it clear you expect people in class every day, you might not need to worry about this, but some schools allow professors to schedule exams outside of class time (which seems super lame to me, but whatever), and I don't know what yours does.

Now of course, on your end, how many reschedules you want to deal with is a factor in deciding if you want to reschedule.