[JeremyBarbosa]

Interesting that there is some research (though only n=11!) on 28h days:

Neurobehavioral Performance in Young Adults Living on a 28-h Day for 6 Weeks

https://pmc.ncbi.nlm.nih.gov/articles/PMC2706904/

[janderson215]

An n of almost 40,000,000 seems pretty substantial to me.