RRULE repeats an event
An RRULE is part of iCalendar recurrence. It works with an event start, duration, time zone, inclusion dates, and exception dates. That makes it appropriate for meetings, reminders, and calendar interoperability.
Cron triggers a job
Cron describes times when a scheduler should start work. It does not carry event duration, attendees, cancellation exceptions, or calendar metadata, and dialects differ in field count and day-of-week behavior.
Daylight saving time needs an explicit decision
A 09:00 local meeting should normally remain at 09:00 when the UTC offset changes. A job that must run every exact 24 hours represents a different requirement. Test skipped and repeated local times around clock changes.
Schedule format comparison
| Need | RRULE | Cron |
|---|---|---|
| Calendar event and attendees | Designed for it | Not represented |
| Server or background job | Requires custom execution logic | Designed for it |
| Exceptions and added dates | EXDATE and RDATE | Usually scheduler-specific |
| Portable syntax | Standardized by iCalendar | Several incompatible dialects |
| Time zone | Event can reference a zone | Depends on scheduler environment |