I Was Born During Daylight Saving Time — Does My Saju Hour Change?

Yes, it changes. During a daylight-saving period, clocks ran an hour ahead of standard time, so you subtract one hour from the clock time to get the real (standard-time) birth hour. For example, someone whose clock read 1:00 PM in July 1988 was actually born at 12:00 PM in real time. Gwiraedang applies this correction automatically for births in the relevant windows, and shows exactly what was corrected on the results screen.

Did Korea actually have daylight saving time?

Yes, three separate times: 1948-1951, 1955-1960, and again around the Seoul Olympics in 1987-1988. That last stretch ran May 10 - October 11, 1987, and May 8 - October 9, 1988 — so people born in those specific windows in 1987 or 1988 are the ones affected. If your registered birth time on your ID falls inside one of these windows, the clocks were running an hour fast during that period.

What happens if the correction isn't applied?

Your Hour Pillar (時柱) can end up one slot off. The Hour Pillar changes every two hours, so if the uncorrected time happens to land near an hour boundary, it gets calculated under the wrong hour entirely. If that boundary falls between 11 PM and 1 AM, it can also overlap with the night Zi hour question — daylight-saving correction is about winding the clock back, while the Zi-hour question is about which convention a calendar follows; they're separate layers of calculation, but the two can meet in the same stretch of time. Gwiraedang calculates consistently even when a correction crosses over into a different date.

How do I know if this applies to me?

If you were born within the windows above, it does. You don't need to memorize any of this — just enter your birthday into Gwiraedang, solar or lunar, either works, and it automatically determines whether a correction applies, showing the details transparently on the results screen if it does. Being born during daylight saving time never meant your Saju was "wrong" — it just meant the clock and the sky were briefly out of step. Correcting for it only makes the chart more accurate — and the chart that comes out of it is, itself, not a fixed fate, just a mirror for reference.