Date: 2 Tammuz 5563
From: Rabbi Moshe Sofer
To: Rabbi Michel Segal
A baby was born at 8:30 PM on a cloudy Shabbos evening, raising doubt whether the birth occurred during daytime or nighttime. The Chasam Sofer rules that according to Rabbeinu Tam's accepted definition of bein hashmashos, 8:30 PM was clearly still daytime, and the milah should proceed on Shabbos as the definitive eighth day.
Source: Shu"t Chasam Sofer OC §80