I know that the Umbraco Cloud docs state: > Before adding a hostname, update your DNS host or domain registrar DNS entries to resolve to umbraco.io So if I add the hostname and then switch the DNS it won't automatically pick up the change? Ideally I want to add the hostname now, then switch the DNS when we're ready to go. Will I have to come back to the Cloud Dashboard to add the hostname in once the DNS has switched?

I'd encourage you to contact Cloud support using the chat bubble in the cloud portal (when you're logged in to https://www.s1.umbraco.io/)