@RampantIvy
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.
DD had an exam on Monday where she started by 10am (opened at 9:30am) and she handed in at just after 9am on Tuesday having not stopped. Several of her friends were similar in doing 24 or nearly hours on the exam. She also had toothache which meant she hadn't slept the night before. Thankfully for her it was the last exam.
She was saying that some people have had to pull out of a second exam which was consecutive days when they've done 20-24 hours on the first exam and just got to about midnight on the second exam and realised they really can't continue.
The quickest time she's taken has been about 15 hours, and I'll admit she's a slow worker, but even those known to be quick are doing that sort of length of time.
And she at one point had 2 exams running concurrently (one started at 2pm, next started at 9:30am the next day, both 24 hours).
I don't think she's minded too much though. She doesn't do too badly not not a lot of sleep and she's far calmer than she was last year when she did exams.
However it is stressful on the parents
. I slept really badly while she was doing them because I was thinking about what if the wifi goes down, or she falls asleep over the work and doesn't hand it in etc... 
Also I had glandular fever in my 3rd year. I would never have managed to do those exams-I was sleeping about 18 hours at day round my finals.