Y'all are too kind.
There's a "conventional wisdom" rule of thumb I've heard before which says that every time zone you cross takes about 1 day to adjust. I don't really buy that per se but, I find that it takes about 2-3 days to adjust each way.
During the 2010s, I was traveling between Sydney and San Francisco for work about 5-6 times a year with occasional trips to South Asia and Europe.
I had a system worked out like this for Eastbound across the International Data Line:Before I would leave for San Francisco, I would get as tired as I could. Whether it was staying out late with friends or staying up late getting everything ready before my trip (paying bills, packing clothes, etc.), or wrapping up projects I needed to finish before my trip.
This allowed me to carry that sleep debt on the plane with me for the 14-15 hour flight to the USA. It's very important that you stay hydrated and eat regularly too.
The one crutch I would use was pre-flight alcohol consumption. I would hit the airline lounge and slam 4 of the highest strength beers I could find (maybe only 3 if it was the Air New Zealand Lounge because they stock good beers). This strategy assured that as soon as I sat down in my seat and they pushed back from the gate, I was out like a light for 90+ minutes at the start of the flight. Then they would serve a meal. Eat it.
After that, it was a mix of watching movies, sleeping, the occasional tour of the airplane, walking around the Economy cabin.
Still on Day 1 because of the International Date Line, you arrive in the USA in the morning (before you left) and it was usually midday by the time I had the rental car and had cleared the airport. I never had any problem going out and running around doing stuff until supper time. After that, you're at a point where your body is starting to wake up for the next day but you've got to go to sleep. If you're tired enough, you should be able to get to bed before midnight. If not, I might drink a few more heavy beers in the hotel bar to help knock me out.
- That's Day 1. You go to bed a good 30 hours after you woke up that morning (on paper)
What you have to watch out for is what I call, "the whip" which happens on Day 3.
- Day 2, you wake up at a semi-normal time in the new time zone. You have to get out of bed and get going on that new day. Do not sleep past 10am. Go about your day, take your meals at the regular lunch and dinner times. Force yourself to go to bed before midnight. You can use some alcohol if you want to. But you have to resist the temptation to stay out late.
- Day 3, you're up at 6am, ready to go to work. This is where it gets dangerous. You run though the day on adrenaline and after dinner that evening, your body decides that two days of trickery is enough and it's going to force you to revert to your Day 0 time zone. So what happens for me is that I can't get to sleep that night. I'll be up until 4am and wake up at 6am to get ready for Day 4 on 2 hours sleep.
- Day 4, power through that day, crash hard that evening, sleep for 8-10 hours and you'll be right as rain for Day 5.
Now reverse the course for the Westbound travel across the International Date Line.For Australia, the flights leave in the evening between 10pm - midnight.
I realize the Japan flights leave midday. Back in Feb. 2020, I flew from IAH-NRT on ANA where we left about 10:30 am and arrived about 4:30 pm the next day.
You'll want to be carrying that sleep deficit so you can get some sleep on the flight.
For Australia flights, I'd pound a few beers, enough to knock me out but not so many that I got knocked out before I boarded the plane.
For Japan, things are pretty normal time wise so no need to try to fall asleep right away.
Same mix of movies, sleep, eat, drink, explore the cabin.
- Day 1 - the day you departed the USA
- Day 2 (or Day 3 if going to Australia. Because of the International Date Line and the late departure from the US, Day 2 never happens) - the day you arrive in the Eastern Hemisphere. On Day 2, the main thing is that you must force yourself to remain awake until 7pm at the bare minimum. 10pm is preferable. Your body is acclimated to US time so it's going to want to start going to sleep early in the afternoon. You must push through that.
- Day 3 - you should be able to wake up at a normal time and proceed through a normal day resisting the urge to go to sleep in the afternoon.
- Day 4 - you should be fully adjusted to the new time zone.
One point of interest in doing this today versus a few years ago, with the limited flights these days, you're probably going to be on a 787 for the long haul which is a good thing. The 787 pressurizes the cabin at 6,000 ft elevation instead of 7,000 feet elevation like you'd find on the older 777 or effectively defunct 747s. Sounds trivial but it does make a difference.
That's my long winded written explanation of how I handle the time adjustment when traveling across the International Date Line. Hope that helps.
In my experience as described here, it is much easier to travel Westbound than it is to travel Eastbound.
