The one day per hour isn't "without being able to power through it" it's for "without a noticeable difference". It's 8pm right now and there's no particular rea

The one day per hour isn't "without being able to power through it" it's for "without a noticeable difference". It's 8pm right now and there's no particular reason I couldn't still be going fairly strong by 4am (if sufficiently motivated), but I will not be as awake as someone adjusted to my 4am being around noon or so. In other words, it's a way to estimate when there will be no tired phase to power through. That said, yeah, an hour a day is a wimpy pace - people modestly used to switching sleep schedules can easily flop much more and be fairly unaffected by crossing the atlantic after a day or two. Being used to it and age both make a big difference. Those who are unused to it or older switch much slower (that would include me at 15 v me at 30). How much the sun matters can also depend, I grew up in near complete darkness during the winter and near 24h sunlight during the summer. My daughter and wife (used to the US continents stable cycle) found that incredibly hard to adjust to, even with dark rooms to sleep in.