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| From | Time difference | Est. adjustment |
| US Eastern | 10h westward | ~7 days |
| US Central | 9h westward | ~7 days |
| US Mountain | 8h westward | ~6 days |
| US Pacific | 7h westward | ~5 days |
| US Alaska | 6h westward | ~5 days |
| US Hawaii | 5h westward | ~4 days |
Seoul runs 9 hours ahead of UTC. The best-case adjustment from US Hawaii takes roughly 4 days; the toughest, from US Eastern, takes roughly 7 days.
It depends on where you're departing from: anywhere from 5 hours (from US Hawaii) up to 10 hours (from US Eastern), since Seoul is a fixed offset from UTC and the gap depends on your home time zone.
Generally the direction with more hours crossed eastward is worse, since your body adjusts to losing time (advancing the clock) more slowly than gaining it (delaying the clock). Check the table above for your specific route's direction.
As a rough rule of thumb, plan on about 4 to 7 days to fully adjust, depending on your departure time zone and how much daylight exposure you get on arrival.
Start shifting your sleep schedule a day or two before departure, stay hydrated and limit alcohol on the flight, set your watch to Seoul time as soon as you board, and get outside into daylight as soon as you land to help reset your body clock faster.