Do you or have you worked there? Neither have I, but friends attest that 9-to-5 is possible there. All depends on the person, their focus and the project they are working on.
I worked at Google for 5 years. 9-5 is possible, though most people work extra hours. The more important issue is the mental energy. 8 hours at Google is different from 8 hours at a low-key tech gig.