The underlying PM reads 3:30PM; the overlying (Station F) reads 12-M. If that indicates 12 midnight, then just before the earthquake struck at 5:12 a.m. on April 18, 1906
In any case it appears to have made its way safely out of the city, and on its way to France.
*International UPU post card rate 2¢
1906 Post Office Report:(An interesting read)https://www.sfgenealogy.org/sf/hist...stoffice.htm
"Station F, located at 2505 Sacramento Street, was uninjured. Besides
the regular forces of three clerks and twenty-five carriers, eight additional
clerks are now employed at this station."
How mail was handled emediately after:https://postalmuseum.si.edu/collect...thquake-mail
Just before (Opened in 1905)
Just after(not mine)
National Register #71000188
United States Post Office and Courthouse
7th and Mission Streets
Built 1893-1905 https://noehill.com/sf/landmarks/nat1971000188.asp