The spec (https://www.freedesktop.org/software/systemd/man/latest/syst...) is more complex than it looks, so it took me way longer than expected to get it working properly. Right now it can only parse time spans and timestamps. I plan to add support for calendar events since I’d like to cover the full spec, but it’s lower prio because I don’t need it myself. If anyone wants to play with it, contributions are welcome :)