What it does: “Schedule — every N seconds” runs a flow on an interval; “Schedule — at a time of day” runs it at a chosen time on chosen weekdays, read in the site’s own timezone. Separately, an allow-list on the Settings screen turns any WordPress hook into a trigger. Notes:

• A stretch of downtime produces one catch-up run, not a backlog; an occurrence a whole period has already passed over is abandoned rather than delivered late. On a site whose wp-cron never runs, a fallback catches up on ordinary page loads.
• Enabling a scheduled flow after today’s time has passed waits for the next occurrence instead of firing immediately.
• Hook arguments arrive in the payload, but objects are recorded as their class and id only — a hook that happens to carry a user or an order cannot write private data into a run.
• Guard rails: hooks that fire on every page load are refused, a watched hook may start at most twenty runs per request, and the allow-list holds at most twenty hooks.