Ask HN: Best API format for recurring schedules?

I'm trying to develop a standard by which people can submit recurring schedules for things like thermostats and access codes for smart locks for seam.co. I couldn't find any standard for recurring schedules other than the iCalendar format, which seems a bit unwieldy for a JSON API.

Cron is a bit limited, e.g. doesn't represent ranges of time.

This seems like a really common problem, anybody solving this in their work today?