Like the IETF, you mean? If I want to implement general internet-compatible timestamps, RFC3339 is right here: https://www.rfc-editor.org/rfc/rfc3339.

How about something big: TCP? RFC9293. It's here: https://www.rfc-editor.org/rfc/rfc9293.

HTML? Different organisation but the same idea, it's over here: https://html.spec.whatwg.org/multipage/

You're reading this web page because of standards organisations that gave everything away for free for anyone to implement.