That’s more on the OS than the text protocol. The protocol doesn’t just hold a text in the ether until it’s time for delivery. A scheduled text is you telling the phone “hey, wait to send this message until it’s time.” Then your phone sends it at the proper time.
iOS still doesn’t have built in text scheduling. There are workarounds, (like using the Shortcuts app to build a “send this text” automation that runs at a specific time), but that’s not the same thing as native support.
Honestly, it would probably be easier to just build a *arr program specifically for downloading YouTube videos directly. Tie it into the rest of the *arr suite, with naming conventions for Plex/Jellyfin.