For servers using local time in regions with daylight saving time, twice a year there are "witching hours" for cron-like scheduling: a task scheduled for between 2:00 (AM, inclusive) and 3:00 (exclusive) will skip a day in the spring, and run twice on a single day in the fall. Unfortunately the @midnight macro in Jenkins is defined as H H(0-2) * * *, which for ⅓ of jobs will trigger the DST problem.
Perhaps it should be redefined as H H(0-1) * * * to avoid this? During upgrade this would cause a one-time occasion when some jobs run 23 hours after the last run, which is not great but probably not a big deal. And it compresses the "midnight" range unnecessarily for servers using (say) UTC.
Minor JENKINS-19977 Build records get confused by timezone changes
Matthew Webber
made changes -