It's not the idea of shipping in six months, it's the idea of shipping something (in six months0 that will be adopted by millions of users.
We don't have the full context of her statement, and I'm guessing (hoping) that she isn't expecting version 1 to be a runaway success, but will allow the team to continue iterating and pivoting, if necessary, before making the determination of whether the project was worthwhile.
I didn't read the quote that way and don't think it's unreasonable to launch an MVP in six months. The other two criteria are business cases against starting and are used to decide which projects should proceed towards their MVPs.
When Google launches a beta (or even alpha), they watch for adoption and "hockey stick" growth. If a project gains traction, the MVP will be augmented with features during the 2-3 years it takes to reach 100M users or $100M.
We don't have the full context of her statement, and I'm guessing (hoping) that she isn't expecting version 1 to be a runaway success, but will allow the team to continue iterating and pivoting, if necessary, before making the determination of whether the project was worthwhile.