"wall-clock time" does not mean what is shown by a literal wall clock. It means the time used by people who are not computer engineers. https://en.wikipedia.org

"wall-clock time" does not mean what is shown by a literal wall clock. It means the time used by people who are not computer engineers. https://en.wikipedia.org/wiki/Elapsed_real_time https://en.wikipedia.org/wiki/Elapsed_real_time When the parent comment said "Wall clock times may occur twice", they meant between 2 and 3am when when leaving DST.