I hope your DD is PK @chocolatenutcase.
I had a very upset DD on the phone the other day, mid exams. They had 24 hours to write 2 x 400 word answers and 2 x 300 word answers for her neuroscience exam. It took her three hours to answer the first one. She had slept badly the night before and was very tired and had a headache. Luckily the next three questions didn't take as long.
One of her friends took 11 hours to answer the first question, then pulled an all nighter to answer the rest, submitting his work just three minutes before the deadline!
In a way these open book 24 hour exams are more stressful then traditional exams. I think in an exam hall the adrenaline keeps you going.