I always thought JP midnight as well, After fishing a lot more lately and actually reaching the cap, I notice that fatigue does seem to follow you into the following day, Especially noticeable when catching popular fish, Having caught 189 Black Sole over the course of a day during a painfully boring day at work the next day when I was attempting to do the same I encountered a staggeringly bad bite rate.
It stuck with me for most the day trying off and on between other things to do until later that night when it started to pick up again to the reasonable expected bite rate and the next day it was back to how I am used to it.
I would be hard pressed with time to test the exact parameters of it but I'm sure there is a separate fatigue system that goes on a larger scale then Soft and Hard fatigue that has been stated stated on previous Fishing related forums.
XI Wiki

