Daylight Savings Time begins on March 9 in 2025, so this day (for most locations in the U.S.) has only 23 hours.

Could there be other factors (such as seasonal variation in the birth rate) that would invalidate this argument? The U.S. birthrate during April, 1997, was 14.3 births per 1000 on an annual basis. The least rate was 13.9 for November, 2.8% less than April. Since a day with 23 hours is 4.2% shorter than one with 24 hours, it seems plausible that March 9 will achieve the minimum in 2025.

(added April 21, 2025) Yow! It seems that there is another factor, and that the correct answer is December 25! Namely, a substantial number of women choose to have medically-advised induced labor shortly after Christmas Day, but the baby fails to cooperate and comes out anyway on Christmas Day. See here.