In the book on page 174, under point 5, Michael writes: “Having a warm bath or hot shower at least an hour before going to bed can also be helpful, as long as you cool down afterwards. It is the drop in body temperature that cues your brain that it is time to sleep. That is also why you should try to sleep in a cool room”.
I don’t think it has to be at least an hour before going to bed. When I was working with dementia residents in a nursing home we found that quite a few of them slept better when they had their shower just before going to bed. And I myself have a nice hot shower just before going to bed and while doing so I think about letting all the worries from the day be washed away… But, our bedroom is cool as we don’t have any heating in it, and I jump into bed without any night attire, so the cool sheets probably do the trick. And then I warm up again and drift off… 😊