One of the features of custom domains, when purchased using " Buy a domain ", was the Transition period. Transition was Blogger, allowing that even with Blogger / Google controlling the domain authoritative servers (which they did, indirectly, by using eNom / GoDaddy as the registrars), and the initial DNS address setup (offered for GoDaddy purchased domains ), the stability of custom domains only starts with the domain authoritative servers, and the Root Name servers . Custom domain published blogs, to be consistently stable, can only rely on the DNS addresses being available on the local DNS servers, on a worldwide basis, 48 to 72 hours after the DNS addresses are added. This built in latency period has nothing to do with how custom domains are designed - and it's an issue over which Blogger and Google have no control.
What Blogger won't tell you