GRE Big Book Test 7 Section 1 Page 270 Long Passage

I feel only I and II are correct. I can’t seem to understand how III is correct.

Saying that III is correct would mean that let’s say if 20% of glucose is returned, then time taken to replenish would be say 50 mins. And if 40% of glucode is returned, then time taken to replenish would be less than 50 mins.
Please bear in mind that the question does not talk about the ‘remaining time’. Otherwise it is obvious that if more percentage of glucose has been returned, the remaining time to replenish would be less.

I do realise that the official answer says that I, II, and III are all correct, and you can’t just challenge ETS, but III just does not sit well with me.

How does this make sense? Surely it should take more time to return a higher percentage of glucose, right? Or am I misunderstanding something?