It doesn't require hours at the protocol level, it's just a social standard. Typically, the first confirmation would occur in ~10 minutes. At the moment, the convention is 6 blocks / 1 hour is sufficient to prevent double-spending, but any merchant could have its own standard.

Also, for something revocable like a domain name, there's nothing preventing Namecheap from giving you the domain name immediately, and then revoking your access to it later if the transaction ultimately fails.