I agree with at least most of the criticism of "Why We Sleep" and haven't read the book. My concerns about messing up circadian rhythms have nothing to do with the book (other than that some of the advice in the book seems to encourage some people to mess up their circadian rhythm). I am disabled due to sleep issues and have met a few others who also have severe issues due to circadian issues (some people with Non-24 do fine if they can keep a Non-24 schedule). It is at least possible that for some people experimenting with a non-24 hour schedule could cause a permanant Non-24 condition so anyone considering trying such a schedule should be aware of the potential risk.

For me (and I'd guess many others) a sleep mask does not make it much easier to sleep during the day. I would need to have a dark environment for a while before sleep. Some people can set up a room like that but I can't at this point. This is not to say that I never get to sleep during the day, but I stay up longer when I go to sleep during the day, even if I have been awake for a while. Some people with Non-24 have the same reaction I do and others don't.