Work out systemd timer schedule instantly with clear inputs, formula shown and shareable results.
systemd timers improve on cron with three controls: AccuracySec lets the kernel batch wakeups to save power, RandomizedDelaySec spreads a fleet's runs to avoid a thundering herd against a shared service, and Persistent catches up missed runs after downtime. Without randomised delay, 400 machines on the same timer all hit the package mirror in the same second.
Timer spread
runs per day = 1440 / interval; effective spread = randomised delay if set, otherwise accuracy; peak concurrency ~ instances x accuracy / spread
Dependency ordering on other units, journal integration, resource limits through the service unit, and no overlapping runs because a service already active will not restart.
It records the last run and executes immediately after boot if a scheduled run was missed, which cron's anacron behaviour only partly provides.