Why east is harder
Your circadian clock runs ~24.2 hours, so it's easier to delay (flying west) than advance (flying east). The common rule: about 1 day of adjustment per timezone hour when flying east, and ~1.5 hours per day when flying west — i.e. 9 hours east ≈ 9 days, 9 hours west ≈ 6 days. Individual variation is huge (age, sleep debt, light exposure), but the direction asymmetry is real and consistent in the research.
The light rules (the part you can act on)
- Eastbound (advance): get bright light in the morning at destination, avoid it in the late evening. Try to sleep on the plane if it's night at destination.
- Westbound (delay): get bright light in the late afternoon/evening at destination, dim mornings. Stay up until a reasonable local bedtime — even if exhausted.
- Anchor your meals to destination time immediately: eating at local mealtimes is a strong zeitgeber (time cue).
- Melatonin (~0.5–3 mg) at local bedtime can help sleep onset; consult a doctor, and don't drive after taking it.
- Hydrate, avoid alcohol on the flight — dehydration amplifies every symptom.
Pre-flight prep
Shift your schedule 1 hour per day toward destination time in the 3–5 days before departure — wake, eat and sleep earlier (east) or later (west). That's the single most effective strategy, and it's free.