I came to it looking for this other remembered fact: "Children who come to Summerhill as kindergardeners attend lessons from the beginning of their stay; but pupils from other schools vow they will never attend any beastly lessons again at any time. They play and cycle and get in people's way, but they fight shy of lessons. This sometimes goes on for months. The recovery time is proportionate to the hatred their last school gave them" while following Pierre Lecomte du Nouy's derivations in his Biological Time.
I'm searching now for more mental recovery time data in the hopes of uncovering something like Nouy's unit.
[by the way, when looking for the bit on time proportions in Summerhill, GoogleBooks couldn't help much, but eklavya.in/pdfs/res delivered. I'll post about their namesake's psychic resonator soon enough.]