YOU CAN MODERATE A QUIZ FOR ONE SINGLE STUDENT.
Step 1 - Click the quiz name.
Step 2 - Click Moderate Quiz from the tabs that appear on the right side of the screen.
Step 3 - Click the box next to the student that you want to moderate quiz times or attempts.
Step 4 - Click the Edit button and add extra time.
Step 5 - Click SAVE.
You have now moderated a quiz for a single student.
I was very frustrated until I figured this out. Hopefully, this explanation is helpful for others.