Cron every day at 2 AM: 0 2 * * * and daylight saving

Two in the morning became the default maintenance window because it is after the evening peak and before the morning one in most consumer facing systems. The expression itself is unremarkable: one minute value, one hour value, and no date restriction, so it runs every night of the year.

The problem is that a lot of timezones make their daylight saving transition in or around this hour. Where the clock jumps forward, the 02:00 wall clock time simply does not exist on that date. Where it falls back, an hour of wall clock time is lived through twice. A schedule pinned to a wall clock hour has to be resolved somehow, and different cron implementations resolve it differently.

Some implementations run a job whose time was skipped once, immediately after the jump. Some skip it. On the repeat, some run once and some run twice. Because you cannot rely on which behaviour you have, the safe designs are to make the job idempotent, to record what it did rather than assuming it ran, or to run the daemon in UTC where no transition exists at all.

If the job must run in local time because it produces a report for humans, move it out of the transition window. 0 4 * * * is just as quiet and is not touched by any common transition rule, which removes the question without any change to what the job does.