Aside from Ekrich - who can at least point to the extracts he has found in historic archives, there are sleep study results that suggest humans still have remnant night waking behaviour; these fall into the intuitive.

Which leaves what I first raised - a thousand years of documented broken sleep by monks in monestaries getting up to pray late at night and again early in the morning.

Some might write that off as hair shirt behaviour by religuous fanatics intent on punishing themselves, others might take it as evidence that people of those times were living with punctuated sleep cycles and those that went to serve their God took to praying when they woke as a matter of course.

There's also the evidence of sleep in Spain and other warmer climes, with additional sleeping during the hottest parts of the day, staying up later, sleeping less during the night and rising earlier before the sun.

It's Ekrich's hobby horse, many niche areas have few champions, but it's not exactly the case that he is drawing on forged entries with no other examples to be found.