Good thinking but this calendar to be available at all times needs to be hosted either by relays or in another server. Hence you don’t really need Nostr to do this.
Best thing I can think of atm is a special note that turns into a widget that you can pin on top of your profile. But we would need to develop a NIP and an API standard for that.
Maybe a bio URL field is the way to go?
The URL should point at a bunch of invoices that represent time slots, the invoices have some kind of API that allows them to drive actions if the invoice is fulfilled; eg create calendar session, initiate order fulfilment?
That’s much more versatile and is essentially a merchant feature for every pubkey!
