How long does it take for a Google domain to become active?

When you register your new Domain name, the new Domain will typically take between 24 to 96 hours to propagate. Once the Domain is propagated, you can setup your Google App Engine application in few minutes.

For More Information Please Refer: https://stackoverflow.com/questions/8087606/how-long-does-it-take-for-a-domain-to-be-fully-implemented-for-a-new-app-engine