Jet lag adaptation plan

Because your body's morning and the clock's morning are different things. Light shifts your rhythm relative to your core body temperature minimum, which falls about two hours before your habitual wake time. Light in the twelve hours BEFORE that point pushes the clock later; light AFTER it pulls the clock earlier. Landing in Tokyo you step into the sun at eight local time, but by your internal clock that is still deep night before the minimum — so that light delays your adjustment instead of speeding it up.

That only happens on shifts of more than eight hours. The clock can be moved either way round the dial: ten hours forward is the same as fourteen hours back. Backwards is faster — roughly an hour and a half a day against one hour — so the long way round is shorter in time. The tool spells this out on its own line so the advice does not look like a bug.

Roughly a day per hour of shift going forward and about two-thirds of that going back. Six hours east is therefore on the order of six days, while six hours west is around four. If the trip is shorter than the adjustment, it is wiser not to shift at all and to keep home time, scheduling meetings around it.

Trial reviews find no difference between 0.5 mg and 5 mg for jet lag, so a large dose buys nothing and more often leaves morning grogginess. Timing matters far more, and it depends on the direction of the shift, which is why the tool puts it in the schedule. Melatonin works as a weak phase-shifter rather than a sleeping pill: it supplements light, it does not replace it.

Yes. Light is the strongest lever available and the schedule works without supplements. Melatonin adds roughly half an hour a day to the shift; tick the box only if you genuinely intend to take it, otherwise it just clutters the plan.

It counts, but it is far weaker than daylight. An overcast sky gives about 10,000 lux, a brightly lit room 300–500, a screen at arm's length only tens. So in a "seek light" window you should go outside, while in an "avoid" window the screen harms mainly by keeping you awake rather than by its brightness.

Approximately. Your temperature minimum is derived from the wake time you entered, so if that was honest the correction is already in. But strong owls and larks spread wider: move the whole schedule an hour or so your way and go by how you feel.