A cron expression names a wall clock time, and wall clock time is neither complete nor
unique. Paste one, pick a zone, and see the whole year at once, including the two days where
the schedule does not mean what it says.
Reading
The year, one cell per day
fire deleted by spring forwardhour happens twiceday does not exist
Next fires from now
In zone
UTC
What to know before you ship it
Where the rules came from, and where the two sources disagree