The amount of time is very long, I don't even actually know what it was, and I personally am not aware of anyone this happened to and have never heard of anyone this happened to. In the past you were expected to hit L5, 2 promotions from hire, and now the expectation is L4, so only 1.
An L5 engineer at Google is someone who is expected to be able to handle any medium-large difficulty task with some amount of cross-team coordination and get it done without much oversight. IMO every software engineer should be able to get to that point in their career eventually otherwise it indicates a pretty big problem.