Well, this is also interesting, because I was born in Ghana and spent the first four years of my life there, and since then have always had insomnia issues, first in the Netherlands and now Sweden. However, the one time I visited Ghana as an adult for a month I slept like a baby.
I actually had a gut feeling that the much quicker shift from day to nighttime darkness and back played a big part in it, but wasn't sure why that might be the case. I assumed it was psychological somehow, that on some subconscious level I felt more "at home" in Ghana's natural environment because it's what my brain was "calibrated" on in the first years of its life. Would be interesting if that actually is the case in a circadian rhythm sense.
> That’s the endogenous period, that really only comes out as is in total darkness over many days.
And speaking of Sweden, I wouldn't be surprised if the short winter days probably do give enough "leeway" to approximate that effect.