Time Difference Between Seoul and Tokyo

Seoul and Tokyo are the same time. Both are UTC+9, neither observes daylight saving, and the flight between them is about two and a half hours. A 4 PM call is 4 PM. People still miss the meeting, and they miss it because the countries do not share a holiday calendar and the matching clocks make that easy to forget. Set both sides to the same hour on purpose once, so nobody adds an hour remembered from a different city.

Korea closes for several days around Chuseok, the harvest festival dated to the lunar calendar, and again around Seollal, the lunar new year. Those weeks are ordinary working weeks in Tokyo. Japan's break around mid-August is not a Korean holiday, and Japan's cluster of public holidays in late April and early May is only partly shared, if at all. A joint deadline set for 'mid-September' or 'the week of the Japanese holidays' needs both calendars open. The lunar dates move by weeks from one year to the next. Do not copy last year's plan.

Because the flight is so short, travelers treat it as domestic and schedule themselves to the minute on both ends. That part is fair: there is no clock change to recover from. The failure mode is the opposite of jet lag. You land on time, in the same hour you left, and walk into a public holiday you did not check. Look at the arrival date on the other country's calendar before you book the afternoon full.