ScheduleRecurrence defines when and how often the schedule repeats.
RFC 5545 recurrence definition combining DTSTART and RRULE properties.
DTSTART specifies the start time and timezone. RRULE defines the recurrence pattern.
Timezone defaults to UTC if unspecified, or if use_site_timezone is true.
Expected format: "DTSTART;TZID=America/New_York:20240101T140000\nRRULE:FREQ=DAILY;INTERVAL=1"