I'll tell you！How long do you taking a bath?

You had better take a bath 1 hour and half after becoming a peak of body temperature after supper, or it is good to take a bath 2-3 hours before sleeping since it becomes sleepy as deep body temperature falls

Then, let's go into about 39 ℃ more tepid hot water slowly before sleeping. Tepid hot water stimulate the parasympathetic nerve and will be in a relaxed state. Hot hot water 42 ℃ or more leads to waking conversely.