GET, POST /schedules; GET, PATCH, DELETE /schedules/{id};
POST /schedules/{id}/pause and /resume.
Fields
Check an expression
POST /cron_previews { cron, timezone?, count? } answers { data: [...] },
the next fire times (at most 10), without creating anything.
A cron expression that does not parse is 422 cron_expression_invalid; a time
zone that is not an IANA name is 422 timezone_invalid.